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THE POTAMOGETONS IN RELATION TO 

POND CULTURE 



A THESIS 
Presented to the Faculty of the Graduate School 
OF Cornell University for the degree of 
DOCTOR OF PHILOSOPHY 



BY 



EMMELINE MOORE 



Reprinted from BULLETIN OP THE BUREAU OF FISHERIES, VoL XXXIII, 1913 
Document No. 816 July 1916 



V 



THE POTAMOGETONS IN RELATION TO 

POND CULTURE 



A THESIS 
Presented to the Faculty of the Graduate School 
OF Cornell University for the degree of 
DOCTOR OF PHILOSOPHY 



BY 

EMMELINE MOORE 



Reprinted from BULLETIN OF THE BUREAU OF FISHERIES, Vol. XXXIII, 1913 
Document No. 815 July 1915 



In escban^e 
Cornell Univ. Library 

NOV 2 4 1915 






o* 



■o 



THE POTAMOGETONS IN RELATION TO POND CULTURE 



By Emmeline Moore 

Contribution from the Department of Limnology, Cornell University 



251 



CONTENTS. 

"^ Page. 

255 

Introduction 2SS 

Historical "' ,50 

Species of Potamogeton investigated ■ ^^^ 

General survey of life conditions of the species investigated •••••■ "^^ 

P. americanus _ ^ ^gj 

P. amplifolius 262 

P. heterophyllus ,g^ 

P. perfoliatus _ 264 

P. crispus 264 

P. zosterifolius 265 

P. obtusifolius 265 

P. filiformis ■ _ 265 

P. pectinatus 267 

P. Robbinsii 26S 

Summary of cultural features 26S 

Natural and artificial propagation ' ' ^^^ 

Propagation by tubers ' 272 

Propagation by tuberous rootstocks ^^^ 

Propagation by subterranean stems not tuberous •••••■ ^^^ 

Propagation by winter buds ^^^ 

Propagation by burs 277 

Propagation by fragments of stems ^^g 

Propagation by seeds 279 

Production of seeds and vegetative propagative structures ['....'. ..... 281 

Economic aspects of Potamogetons ^g^ 

Species of Potamogeton and the animals foraging upon them '.''''.'.'.... 285 

Conclusion 286 

Bibliography 289 

Explanation of plates 



THE POTAMOGETONS IN RELATION TO POND CULTURE. 



By EMMELINE MOORE, 
Contribution from the Department of Limnology, Cornell University. 

J- 
INTRODUCTION. 

The cultivation of lakes, ponds, and streams follows as a natural consequence the 
biological investigation of the aquatic life within them. Herbivores and carnivores 
live their life in the water, and if we ponder over their means of sustenance we are 
struck by the fact that the natural food supply has rarely been augmented by cultural 
methods. 

"The larger aquatic plants," says Pond (1903), "form a link in the chain of nutri- 
tive relations that stretches from the water and soil to the higher fishes." If such is the 
importance of these plants, the great mass of vegetation which comes to maturity each 
season is a national asset. Yet the annual yield has never been estimated or given a 
place in the Government crop reports. 

Aquatic plants have contested for possession of the waters much as the grasses 
have contended for supremacy on land, until it may be said that the dominant forage 
crop of our lakes, ponds, and streams is to be found among the pondweeds, the Pota- 
mogetons. Variety in form, adaptability to environment, and diversit)' in range have 
all contributed their share in giving prominence to this group and in furthering a natu- 
ral resource whose propagation and control are vital factors in the economic relations 
of the life of inland waters. 

The object of this investigation is to present such observations and experiments 
on the natural and artificial propagation of the Potamogetons as will render cultural 
methods economical and practical. 

The work herein recorded was carried on at Cornell University under the direction 
of Dr. James G. Needham, to whom I wisli to express my grateful thanks for help and 
suggestion. 

HISTORICAL. 

The cultivation of aquatic plants was an ancient occupation, one which concerned 
itself with the beautification of pools and fountains. In modern times, too, aquatic 
plants have been used in variety and profusion in the ornamentation of artificial or 
natural ponds. But the cultivation of aquatics from an economic standpoint is a new 
idea, so new, in fact, that data regarding it are just beginning to appear in bulletin 
form in the Government compilations of scattered and isolated experiments. In the 
bulletins plants of the genus Potamogeton have received the larger measure of notice 
because observations on the feeding habits of animals associated with them point to 
the important role of these plants in the economy of nature. 

=55 



256 BULLETIN OF THE BUREAU OF FISHERIES. 

Further contribution to the present status of the Potamogetons incorporates of 
necessity a considerable body of observation pertaining to the systematic, morpho- 
logical, and biological aspects of this group, and renders it highly desirable to set forth 
the historical background of each of these three phases of the subject. 

John Gerardi;, 1633. 

A lioginning in tht classification of the Potamogetons was made by the old herbalists, medical 
men, who found it neccssarv' to study plants in detail in order to discriminate the kinds employed for 
different purposes. The special virtue in Potamogetons, for example, resided in tlie leaves, which 
were applied to reduce inflammation. In the herbal of John Gerarde the group Potamogeton (I'ola- 
mogeiion in Uie old spelling and pondweed or water spike in the common parlance of the time) con- 
sisted of four species — a Ijroad-leaved pondweed, a n;uTow-leaved pondweed, a small pondweed, and 
a long sharp-leaved pondweed. There was a figure of the entire plant accompanied by the Latin and 
English name. Then followed the "description, place, time, names, nature, and virtues agreeing 
with the best received opinions." A "fennel-leaved water milfoile" illustrated by a figure easily 
recognized as our fennel-leaved pondweed, Potamogeton pcclinaius, was given a place among the 
Myriophyllums. Such was one of the earliest attempts to classify the group. 

Chamisso and Schlechtendal, 1827. 

The first im]5ortant monograph of the Potamogetons was tlie work of Chamisso and Schlechtendal, 
who, in Linnea, volume 2, 1827, systematized the results of scientific obsen-ation during the latter 
part of tlie eighteentli and the beginning of the nineteenth centuries. Under the family name of 
AlismaccEe 21 species were described and illustrated by drawings of fruit and leaf, including among 
them many of the common and widely distributed species of to-day. Several other Potamogetons 
were listed as uncertain in position and difficult to chissify, a condition which holds as true to-day as 
then, when Chamisso and Schlechtendal struggled to bring order out of chaos in this puzzling group 
and recorded this pertinent obser%-ation : "Species Potamogetonum habitum mutantes in alias sa;pe 
transire videntur, aliensque speciei habitum mentientes serutatorum irrident," which translated 
is, "vSpeeies of Potamogeton changing their habit seem often to pass into others, and feigning the habit 
of other species baffle research. " 

Reichenb.\ch, 1845. 

Reiclienbach 's monograph of the Potamogetons, in Iiis Icones Florse Germanicas et Helveticae, 
followed in 1845. More intensive in scope than any preceding work, it marked a distinct advance 
both in the method of description and in the matter of illustration. Several reproductions, especially 
of flower and fruit, which were drawn with great clearness and accuracy, have found their way in the 
latest authoritative works on the subject. In this monograph the author introduced the figure of the 
so-called "bur," the vegetative propagative body of P. crispus Linnaeus, though he apparently did 
not recognize its signific;mce in the rapid propagation of this species. It is interesting to note that 
the figure is inserted without further description or comment. Moreover, it is erroneously drawn, and 
the error has been copied time without end. 

Irmisch, 1851. 

Thilo Irmisch, in a published note in Flora, 1S51, first recognized tlie presence of tubers on P. 
pcctiuatus. 

Agardh, 1852. 

A year later J. C. Agardh, in Verhandlungen der K. Schwedischen Akaderriie der Wissenschaften, 
recorded several observations on the tubers of this species of Potamogeton. 

Clos, D., 1856. 

D. Clos was the first to publish an account of the origin of tlic "bur" of cri'ipui, though his obser- 
vations are incomplete regarding both their development and their germination. 

Irmisch, 1858. 

In a remarkable monograph by Irmisch, Uber einige Arten aus der naturlichen Pflanzenfamilie der 
Potamogeton, the history of the development of the tuberous growths on P. pectinatus is recorded and 
their morphological and anatomical structure described. The author states that, at tlie end of tlie vegeta- 



POTAMOGETONS IN RELATION TO POND CULTURE. 257 

tive period in tlie fall, the shoots of recent formation have a singular appearance, the last two thin 
internodes bearing tubers at the end. At first the tuberousend resembles a conical terminal shoot or bud 
surrounded by scales. Internodes make their appearance and soon become thickened ; eventually the 
scales split and disclose a tuber of two swollen internodes. Simultaneously a slender bud forms at the 
distal end of the tuber, and axial outgrowths develop from the sides that bespeak the shoots of ordinary 
branches. These axial shoots in turn develop swollen internodes which follow two thinner ones as in the 
preceding case and produce a scries of tubers dichasial in form. The excellent series of drawings by 
means of which the author depicts tlie transition from intcmode to tuber leaves notliing to be desired 
in the morphological interpretation of them. They are clearly two modified internodes. 

Tuber-bearing shoots grow out of the upper leaf axils also, and follow the usual development of genera- 
tions of internodes with leafy shoots, besides the tuber-bearing ones in two or three series. The anatom- 
ical structure of the tuber resembles that of the stem excepting that all tissue not fibro- vascular is filled 
with starch. The observations on P. obtusifolius are incomplete, but the presence of winter buds is 
noted. For P. nalans and P. hicens the morphology of the rootstock, stem, and shoot is completely 
determined, and the details are clearly shown in the drawings. The method of branching is fundamen- 
tally tlie same in tlie two species. In brief, the growing tips of the rootstocks branch dichotomously, 
giving an erect axis and a horizontal one. Each generation of the developing rootstock brings forth two 
horizontal internodes and a bud which is the incipient erect axis. The terminal bud at the end of the 
horizontal axis reproduces this condition as long as the plant lives. In the development of the erect 
shoot, the scales, usually three in number, grade into stipular sheath, phyllodes, and foliage leaves. A 
two-fifths arrangement of leaves is noted and the shoots follow the same order. The winter condition 
of P. hicens consists of rootstocks by means of which the plant propagates itself rapidly in the spring. 
The internodes of these rootstocks are shorter and tliicker than tlie ordinar>' ones and are borne in a suc- 
cession of three or more with terminal and axillarj' buds containing Uie incipient axes of the horizontal 
and erect shoots. 

Irmisch made observations also on P. crispus, investigating especially the "burs" or propagative 
shoots, although this work was anticipated in part by D. Clos in his Mode de Propagation particulier au 
Polamogeton crispus L. Irmisch, however, found two forms of the burof (:n.t/>!(.t, the slender spicular bur 
as well as the stout, homy, denticulate one observed by Clos. The former bur he observed growing in 
the axils of detached shoots in late autumn and afterwards breaking away from the axils and settling in 
the mud. The origin of the latter form he did not observe, but he found it in the muddy bottoms of 
ponds in great abundance. These "burs" or modified twigs, as Irmisch sometimes called them, he con- 
sidered important examples of propagative structures. 

In connection with these plants, Irmisch first pointed out the "Scheiden-Schiippchen, squamulae 
intravaginales, " scale-like structures developed at the leaf bases, having as a possible function the pro- 
duction of slime or mucilage for the protection of young and slender shoots. 

This monograph is of special importance in presenting the morphological data of a few species of 
Potamogeton. From time to time further contributions have been made to the subject by other investi- 
gators in the field, but this still remains the greatest work of its kind. 

As a result of these studies on the tubers of P. peciinatus, the rootstocks of P. lucciis. and the burs of 
P. crispus, Irmisch came to appreciate the advantage of artificial propagation in this group and remarked 
in conclusion, in an observation tliat is prophetic of present day interest, "That many of the Potamoge- 
tons, as well as other aquatic plants, possess in a singidar way that possibility of domestication which 
has given us the tame animals from the wild ones. " 

ROBBINS, 1S67. 

Thus far the work of the Potamogetons was confined principally to European species. In 1867, 
however, the American species were reduced to something like a complete intelligible systematic shape 
by Dr. G. W. Robbins, whose descriptions, a", far as they came within the range, were incorporated in 
Gray's Manual, edition 5. Later descriptions of the western species were published as they became 
known. 

MORONG, 1893. 

The greatest contribution to the literature on the North American species of Potamogeton is by 
Thomas Morong in his Naiadaceae of North America, a monograph which includes 37 North American 
species, 14 of which are confined to this country. Many of these species were studied through succes- 
86309°— 1.5 2 25s 



258 BULLETIN OF THE BUREAU OF FISHERIES. 

sive. seasons of the year and a considerable body of knowledge pertaining to the development of the 
plants was accumulated. It is recorded that 17 of the described species are propagated vegetatively by 
one or more of the following structures: Rootstocks, tubers, winter buds, and stems. 

SauvagEau, 1894. 

The work of Sauvageau is particularly a contribution to the biology of the Potamogctons. While 
there are additions in morphology and anatomy extending the observations of Irmisch to other members 
of the genus, the most notewortliy investigations pertain to the origin and the development of those 
vegetative stnictures which greatl)' facilitate the multiplication of species during the vegetative 
period. 

Sauvageau devotes a special memoir to P. crisf'us. He observed both forms of the so-called "burs" 
of this species, the slender spicular one and the more common denticulate one, noting tlieir origin, 
growth, and germination. 

Experiments conducted in aquaria show that detached fragments of stems of various forms as 
P. lucens, P. detisus, P. perfoliatus, and P. crispus develop roots, shoots, and buds, and that such 
detached parts of plants constitute a rapid means of propagation. Investigation of the growth habit of 
P. natans discloses a condition in marked contrast to the above-mentioned species. No special propaga- 
tive bodies exist, but tlie species perpetuates itself by the continuance of the rhizome anchored in 
the mud, a rhizome which maintains itself through the winter rest period with the submersed shoots 
in various stages of growth . 

Experiments on seed germination indicate a latent period of considerable variability. In P. crispus 
germination occurs within a year; in P. natans in from three to four years. 

Fryer, 1900. 

The first two installments of a fine quarto work. The Potamogctons of the British Isles, by Alfred 
Fryer, appeared in 1900. The monograph includes the vary'ing forms and states as well as the recog- 
nized species, with accompanying plates, by the artist, Robert Morgan, who has reproduced the plants 
in color with singular beauty and accuracy. Unfortimately for science, the author's death occurred 
before this important work was finished. 

Fryer had an intimate acquaintance with the Potamogctons and their habits. He grew many speci- 
mens in tanks in his garden, watching developments there and in their native haunts at difTerent times 
of the year. He grew Potamogctons in order better to classify them, for he recognized the necessity of 
having a long series of specimens of the same form. " One set, " as he says, " would contain a series of 
forms from lucens to heUrophyllus without a single gap. This would show the way in which two quite 
distinct species pass from one to the other without a missing link. " As a result of these observations a 
long and valuable scries of communications on the genus, ixnder the title "Notes on Pondweeds, " 
appeared in the Journal of Botany from 18S3 to 1899. 

Bennett, 1880-1914. 

In the Joiunal of Botany Mr. Arthur Bennett's "Notes on Pondweeds" have appeared regularly 
from 1880 to the present time. He has become the acknowledged authority on the classification of the 
genus. 

PiETERS, 1902. 

In a Contribution to the Biolog>' of the Great Lakes, Mr. A. J. Pieters notes the distribution of 
aquatic plants, describes the forms occurring in diverse situations, presents details of structure , and 
records various methods of vegetative reproduction. The Potamogctons, he observes, form a conspic- 
uous feature of the aquatic vegetation, predominating, as a rule, in aquatic associations or flourishing in 
isolated patches. P. heterophyllus, he says, exemplifies the latter condition in that it thrives in a surf- 
beaten sandbar, where its runners ramify in all directions among the stones and pebbles, and its roots 
penetrate the tmderlying clay. Details of structure which are figured for P. americanus suggest the 
special adaptation of a thin, broad-leaved form, whose leaves are submerged, for withstanding diminu- 
tion of light and rapid motion of W'ater. The so-called hibemacula, or winter buds, represent the more 
familiar forms of vegetative reproduction observed by the author. 

Pond, 1903. 

Further contributions to the biological literature of aquatic plants have been made by R. H. Pond. 
Two papers are presented on this subject. In the first. The Biological Relation of Aquatic Plants to the 



POTAMOGETONS IN RELATION TO POND CULTURE. 259 

Substratum, tlie author showed that rooted aquatics depend on the soil substratum for the supply of 
nitrates. In conducting the experiments various aquatic plants were used, among which were P. per- 
foliatus and P. obiusifoUus. It was found that both of these plants are dependent on the soil substratum 
for optimum growth, though the cuttings which were employed behaved differently in manner of growth: 
P. perfoliatus showed an increase of growth through the development of new rhizomes; P. obiusifoUus 
manifested it in a continuation of the branches already present. The behavior of P. perfoliatus is in 
accord with the observations of Sauvageau in his experiments on the propagation of Potamogetons by 
fragments of stems. 

The second paper of the author, The Larger Aquatic Vegetation, to appear in Ward's American 
Fresh-water Biology, supplements the work of the first by additional observations, discussions, and 
generalizations. From his observations on the substratum of the larger aquatics it appears that they 
may be found growing on gravelly, sandy, or loamy soil, the loamy soil supporting the greatest variety 
of species. Direct experiments on this point, with the natural conditions reproduced as nearly as 
possible, bear out this observation. The author states, moreover, that the character of the soil is so 
important a factor that it is possible to predict the nature of the bottom from the species that are found 
growing in it. For example, "Among the islands of western Lake Erie Potamogeton heterophyllus is 
common on the reefs and pebbly shores, but it is not noticeable in the coves where a good soil sub- 
stratum exists, and so prominent is it in the former places that its presence may be considered char- 
acteristic of the flora." 

JEPSO.N, 1905. 

In a popular article in the Sunset Magazine for February, 1905, Prof. W. L. Jepson has set forth the 
possibilities of the marshes as a feeding ground for ducks. He has taken as a concrete illustration the 
Suisun Marshes in California, marshes which abound in the fennel-leaved pondweed, P. pectinatus, 
and which afford natural feeding grounds for the various kinds of wild ducks, more particularly the 
canvasbacks. The canvasback and the broadbill, both diving ducks which visit these marshes, devour 
greedily the tubers that are developed in abundance on the rootstocks and upper portions of the stems 
of this Potamogeton in the autumn. It is claimed that these tubers give the fine nutty flavor to the 
canvasback at this season of the year. Other ducks, nondiving species, feed on the tender rootstocks 
and leafy stems which are brought to the surface in the feeding operations. 

ASCHERSON AND GrAEBNER, 1907. 

Ascherson and Graebner have published the last important monograph on the group, the Potamo- 
getonacea;, in Das Pflanzenrelch. In this work the whole number of the described species has reached 
87. Of these North America has 38, 14 of which are exclusively American. The numerous forms and 
varieties that are listed, though some common ones are omitted, illustrate how difficult the problem 
of classifying the Potamogetons still remains. In addition to the literature on classification the authors 
have assembled much important data on the anatomy and morphology of the group from foreign sources 
not generally accessible. Under the caption, tjberwintenmgsformen und Vegetative Vermehnmg bei 
Potamogeton, the following propagative structures are figiu-ed: The slender, spicular bur of P. crispus; 
the large denticulate bur of P. crispus; the tuberous rhizome of P. lucens; the tubers of P. pectinatus; 
and the winter bud of P. obiusifoUus. All except the first are reproductions of Irmisch's celebrated 
monograph. 

McAtee, 191 1. 

In a bulletin of the Biological Survey entitled Three Important Wild Duck Foods, Mr. McAtee has 
assembled for Government publication important data regarding these foods, in the hope that they may 
Decome more widely known and propagated for the preservation of wild ducks. Analyses of the food 
content in the stomachs of the more important species of the game ducks show that the pondweeds. the 
Potamogetons, are a favorite plant food. The ducks which apparently show a special fondness for it 
are the canvasback, the redhead, the scaup, and others, the first of which takes a very large proportion 
of the Potamogeton, the amount being nearly 50 per cent of the food eaten. 

The best known duck food among the Potamogetons is P. pectinatus, of which the seeds, the tender 
rootstocks, and the tubers are eaten. It is general in distribution, thriving in fresh, brackish, or salt 
water. This and other widely distributed species are figured, and suggestions on how, when, and where 
to plant them are given. 



26o BUI^IvETIN OF THE BUREAU OF FISHERIES. 

MiCKLE, 1912. 

A Canadian bulletin, The Possibilities of Northern Ontario as a Breeding Ground for Ducks, by 
G. R. Mickle, is an investigation of the shoal waters of that Province with a view to their utilization 
for the propagation of wild game. In the preliminary survey the approximate amount of shoal waters 
is estimated to be 2,800,000 acres, on which various edible water plants grow. But it is hoped that 
the natural supply may be augmented considerably by transplanting such of the larger aquatics as will 
contribute especially to the food of wild ducks. Among the valuable water plants suitable for trans- 
planting, the autlior names several species of Potamogeton. P. natans, because of its abundant seed 
habit, P. perfoliatus and P. crispus because of their edible leaves. 

Mickle and Thompson, 1913. 

A second Canadian bulletin by G. R. Mickle, written in collaboration with R. B. Thompson, 
supplements the work already done in this line. A table giving the estimated percentages of the 
various constituents of duck food shows that both P. heterophylliis and P. perfoliatus form an im- 
portant food constituent in the diet of wild ducks. 

It will be seen from the foregoing resume of the literature on the genus Potamoge- 
ton, that an important extension of the subject is in the field of biologic research, an 
aspect of the study which regards also the economic significance of the group. It is 
apparent, too, that this field of research concerns itself primarily with the propagation 
of Potamogeton by such structures as tend readily and effectually to distribute the 
group, viz, by burs, tubers, rootstocks, and winter buds. These have been described 
generallv in Europe and in America, and one may consider their production a natural 

phenomenon. 

SPECIES OF POTAMOGETON INVESTIGATED. 

The species which are included in this in\'estigatiou lia\'e been selected from the more 
or less common forms growing in the lakes and ponds at Ithaca, N. Y., and vicinity 
(Spencer and North Fairhaven). And these species have been chosen because they 
offer variety in habitat and in methods of propagation, and because they ser\-e an 
important role in the economic relations of aquatic life, affording food, shelter, and 
support to many forms of animals which exist among them. The list of species follows: 



P. americanus C. and S. 

P. amplifoliiis Tuckerm. 

P. hcierophyllus forma tcrrhtris Schlechtd. 

P. perfoliatus L. 

P. crispus L. 



P. zosterifolius Schumacher. 
P. obiusifolius M. and K. 
P. filiformis Pers. 
P. pectinatus L. 
P. Robbinsii Oakes. 



These Potamogetons were studied from September, 1912, to June 1914, in their 
natural habitats and in aquaria. Entire plants were thus obser\-ed throughout the 
period of development of those structures which are valuable in the vegetative propa- 
gation of the species. From time to time collections were made of entire plants with 
their subterranean systems intact. In shallow waters the plants were uprooted by 
hand, but in the deeper waters they were obtained by means of a rake or a grapple 
thrown over the side or the stern of a rowboat. No collections were made in mid- 
winter, i. e., from the latter part of December to the middle of February, when the 
frozen condition of the lakes and streams rendered it impracticable. P. crispus is an 
exception, since it was collected from spring pools at all times of the year. 

These studies have afforded an opportunity to observe the animals that are inti- 
mately associated with the Potamogetons. Such have been noted, especially those 
forms which depend upon these plants for food, support, or shelter. 



POTAMOGETONS IN RELATION TO POND CULTURE. 261 

GENERAL SURVEY OF LIFE CONDITIONS OF THE SPECIES INVESTIGATED. 

POTAMOGETON AMERICANUS. 

This species, which has been grown from seed and cultivated through two succes- 
sive seasons, will receive more specific treatment later under the caption "Natural 
and artificial propagation." In its natural habitat this plant has been obser\'ed 
growing near the mouth of Fall Creek, a tributary of Lake Cayuga, and in a near-by 
cove of the lake, at varying depths of 3 to 4 feet. It has been observed also at Spencer 
Lake, at about the same depth but in much swifter water. In the latter situation 
the blades of the leaves are conspicuously attenuated. According to Fryer (1900), 
who has observed this plant in various localities, it is a plant of upland streams and 
rivers rather than of stagnant waters. 

By uprooting the entire plant in the growing season, it is found that the stem 
springs from a rootstock that is deeply anchored in the mud, where new shoots radiate 
horizontally from the established parts of the plant. During the summer these young 
rootstocks produce large buds at their tips (fig. 6). After the plant dies down, which 
may occur as early as August, the subterranean system remains intact for several 
weeks. The new rootstocks, however, carrying the buds at the tips, become eventually 
detached through the disorganization of the parent stem and in time die away, leaving 
but little beyond the isolated buds to perpetuate the plant the following spring. Such 
buds, since they remain in a quiescent state during the winter, may be called winter 
buds or hibernacula, a term applied to structures of a similar nature and function. 
Mr. A. J. Pieters (1901) doubtless referred to propagative structures of this kind when 
he recorded for P. americanus (P. lonchites) "extensive runners bearing buds at their 
ends," though no figures are given and no further observations are noted. 

Fryer (1888) mentions an autumnal state of P. americanus {P. fluiians) in which 
the leaves are all narrowly linear or grasslike. These later growths, he says, are 
developed in the axils of old leaves during the natural decay of the lower part of the 
stem. They are ultimately set free as fascicles of narrow leaves which, after rootlets 
are formed at the base of the new growth, sink to the bottom and continue the life of 
the species. Such structures, which would be analogous to the winter buds of P. obtu- 
sijolius and P. zosterif alius , have not been observed in P. americanus under investiga- 
tion, though they may have been overlooked in the changes of water level during the 
autumn. 

POTAMOGETON AMPLIFOLIUS. 

This is an American species distributed quite generally throughout the continent. 
It forms large patches in the open vegetation but thrives also in close association with 
P. Rohbinsii, Heteranthera dubia, Ceratophyllum deniersum, Elodea canadensis, and 
other plants of aquatic meadows. As a forage plant it may be regarded as one of the 
best, growing continuously from early spring to late fall or early winter and producing 
an abundant herbage by reason of its numerous large leaves. The rankest growths 
have been found in the more quiet waters of Lake Cayuga and "The Pond" at North 
Fairhaven, at depths of 5 to 7 feet, in a substratum of mud rich in vegetable mold. 
Propagation is rapid. The dense patches of stems, more or less unbranched, arise in 
great numbers from an intricately developed subterranean system Cfig. 7). This 



262 BULLETIN OF THE BUREAU OF FISHERIES. 

extensive ramification of underground stems, richly provisioned with starch, remains 
more or less intact during the winter, carrying at alternate nodes undeveloped shoots 
which quickly establish new extensions of the plant in the spring. Another means of 
vegetative propagation is found in the detached tips of branches which, after separation 
from the decaying parent stem in the fall or spring, sink to the bottom and become new 
centers of growth. New shoots also develop at the nodes of decaying stems and, on 
separation, sink to the bottom and take root as in the case of detached tips and stems. 
Besides these vegetative means of growth this Potamogeton produces an abundance of 
seeds. 

POTAMOGETON HEvTEROPHYLLUS. 

Various forms of this species occur throughout almost all of North America except 
the extreme north. One of the numerous forms, /orma krrestris Schlectd., is repre- 
sented in this investigation and all data herein recorded pertain to this plant. It is a 
so-called land form of Potamogeton and briefly characterized in Gray, seventh edition, 
as "freely creeping in exsiccated places, producing numerous branches which bear tufts 
of oblong or oval coriaceous leaves but no fruit." This plant, which grows in the open 
air after being left entirely uncovered by water, has been observed in two places along 
the shores of Lake Cayuga — one in a railroad pool 2 miles east of Ludlow\'ille and the 
other on a sandbar at Myers Point. In each of these places it is interesting to note 
that gradations in habit accompany the varying changes in habitat. The railroad 
pool is a particularly favorable spot for the growth of this Potamogeton. It is an 
artificial pond which has been developed by building a railroad embankment near the 
foot of the bluff bordering the lake. In consequence, a long, trough-like depression 
exists between the bluff on one side and the railroad embankment on the other, with 
water from the lake seeping through and maintaining itself at about the level of the 
lake. It is a situation especially favorable to the growth of this plant, because the 
annual withdrawal of the water is gradual, following the natural lowering of the lake level 
during the summer months. The bottom of the pool is covered with black mud, largely 
marl in composition, a foot or more in thickness, over which water may rise to the height 
of 12 to 16 inches. During high-water level in the spring, this Potamogeton grows 
submerged in the pond with its tuberous rootstalks anchored in the mud (fig. 8). Upon 
the withdrawal of the water, following the lowering of the lake level in the summer, 
drought conditions prevail, and then the submerged leafy stems give place to the land 
forms. Upon the approach of drought conditions the previously submerged leaves die 
and from the main rootstock or from those arising from the axils of the lower leaves 
(upper in some cases, Bennett, 1880) runners extend horizontally to a depth of 2 to 6 
inches below the surt"ace of the mud. From the fertile nodes of these runners erect 
axes arise, bearing tufts or rosettes of leaves which cover the ground in great numbers 
and compete with mosses and small forms of sedges, carpeting the surface of the mud. 
The leaves of the rosette (fig. 12) are unlike the elongated, membranous, submerged ones. 
They are more rounded in form and coriaceous in texture, and by the presence of sto- 
mates on the upper surface of the lamina, they are enabled to function as ordinary 
leaves. 



POTAMOGETONS IN RELATION TO POND CULTURE. 263 

During the season of 1913 the plants which flourished in a submerged condition 
during the month of May gradually changed their habitat upon the withdrawal of the 
water during June and became land forms by the first of July. At this time the tuberous 
rootstocks which perpetuate the plant vegetatively were well developed, and waited 
only the final stages in the curing process to become the perfected vegetative structures 
which tide this species over the unfavorable season of growth. 

On the sand bar at Myers Point, the other station where this Potamogeton thrives, 
the life conditions are not so sharply marked by the complete withdrawal of the water 
during the dry season, and the various stages exhibited in the transmutation from aquatic 
to land forms were easily observed. In water about 10 inches deep the continuously 
submerged plants developed low bushy stems, with a fc^v coriaceous leaves at the top. 
In shallower water the plants behaved in the same way, producing bushy, stunted- 
looking stems, which finally graded into land form with leaves in tufts or rosettes resting 
on the exposed surface of the sand bar. The rootstocks, which were twisted and con- 
torted in their effort to become established in the pebbly and gravelly sand bar, were 
buried from 2 to 4 inches beneath the surface in the rich, black soil of the bar. AH 
of the internodes of these subterranean stems were more or less thickened and often 
attained a length of 8 to 14 inches. 

No fruiting plants were found, and this observation is in accordance with the 
generally accepted opinion that this form of hcterophyllus is propagated entirely by 
vegetative means. Observations on the artificial propagation of this species are recorded 
in a later chapter of this paper. 

POTAMOGETON PERKOLI.ATUS. 

The leaves of this plant afford valuable forage material, though the season of 
growth is comparatively short, the plants appearing late in the spring and dying quite 
early in the autumn. In the environs of Ithaca this species flourishes in quiet waters 
either in a substratum of sand at the relatively shallow depths of 2 to 3 feet, or in 
"aquatic meadows" in a substratum of mud at depths of 3 to 5 feet. The observa- 
tions of Pieters (1901), in "The Plants of Lake Clair," and of Tliompson (1897), in 
"The Biological Examination of Lake Michigan" extend the range of depth at which 
this species exists to 12 feet. During the growing season the vigorous undergronnd 
stems increase rapidly the output of forage material, since a single subterranean system 
produces a large number of erect, much branched, leafy stems. The experiments of 
Pond (1903) and Sauvageau (1894) and the obser\-ations of R. B. Thompson (1913) 
afford evidence of other means whereby the rapid extension of this plant takes place. 
In accordance with their observations, young branches, which are easily detachable, 
float away and rapidly become new centers of growth. In winter the vigorous and 
abundant subterranean system decays, leaving only the terminal shoots of two or 
three nodes (Fryer, 1900) to continue the plant the following spring. This plant, 
therefore, has three important means of vegetative propagation: By readily detached 
leafy stems, and by extensions of the subterranean system, both of which operate to 
multiply the plants during the growing season; and by the terminal portions of root- 
stocks which, remaining in a quiescent state during the winter, establish new plants 
in the spring. 



264 BULLETIN OF THE BUREAU OF FISHERIES. 

POTAMOGETON CRISPUS. 

This species, a native of Europe, was recorded in this country by Pursh as early 
as 1814 (Arthur Bennett, 1901). Since that time it has become estabUshed over an 
extensive area because of the remarkable facility for multiplying itself vegetatively. 
It is the most abundant Potamogeton in the vicinity of Ithaca, where it flourishes in 
various habitats — in deep or shallow water, in sand or mud bottoms, and in stagnant 
pools or flowing streams. It is singularly adaptive in each situation. It has been 
collected with P. pectinatns growing at depths of 8 feet, in which habitat the internodes 
are extremely elongate; it has been found in pools where the substratum is an accu- 
mulation of debris from ash heaps and dumping grounds; and it is not uncommon in 
the swifter parts of streams and along the lake shore in sandy situations where the 
substratum is thrown into ripples by wave and current action. In the latter situation 
it has always possessed short, stocky stems and a general dwarfish appearance. 

P. crispus grows the year round and spreads with great rapidity. It is propagated 
primarily by "burs," peculiarly distinctive structures to which there is nothing quite 
comparable in our native species. Morphologically they are branches, but in the stage 
most frequently seen they are scarcely recognizable as such members of the plant 
structure. They have a homy look and a reddish color. The shortened internodes 
and thickened persistent leaf bases combine to give the characteristic bur-like appear- 
ance (fig. 22). 

POT.^MOGETON ZOSTERIFOLirs. 

This flat, grass-like species of Potamogeton is not largely foraged upon bv aquatic 
herbivores, yet it appears in greater or less abundance in most ponds and lakes and 
doubtless serves an important role in the economy of life by furnishing support and 
shelter to the countless small forms which have been found upon it. 

P. zosicrijolius is among the earliest of the Potamogetons to appear in the spring, as 
well as among the first of them to disappear in the autumn. It flourishes in a sub- 
stratum of mud in still or running waters, and while it is not adapted to possess the soil 
so completely as P. crispus, nevertheless it has effective means of perpetuating itself. 
Mr. A. J. Pieters (1901) remarks that this species, which he has observed growing in 
abundance in Lake Erie, may be losing the power to produce seeds. Indeed, during the 
past season few plants matured seeds in the several regions where they were observed, 
but all developed winter buds in great abundance (fig. 33). 

Large quantities of vegetation, that is, the accumulation of the varied and abundant 
mass that still exists in the autumn, have been hauled up to the surface for examination, 
and it was both surprising and astonishing to see the vast number of winter buds of 
this Potamogeton that were entangled among the stems of other plants. It suggests to 
an extent how well this species accommodates itself to its surroundings. It never 
forms dense patches of growth, but it often occurs with aquatic plants that form them 
more or less densely. By virtue of its slender, grasslike habit, it occupies the interstices 
of the more rank aquatic flora, and it occupies these spaces as simple individual plants, 
not as erect axes of a complete and intricate subterranean system. The plants are 
anchored to the substratum by the roots only, which develop from the winter bud, and 
because of this loose hold in the soil they are readily pulled up. The large number of 



POTAMOGETONS IN RELATION TO POND CULTURE. 265 

plants which have been uprooted appeared always to possess a comparatively simple, 
erect stem which developed from a winter bud without the ramifications of rootstock 
which are characteristic of other species of Potamogeton not grasslike in habit. 

POT.\MOGETON OBTUSIFOLIUS. 

This species is apparently an important aquatic forage plant, for its delicate leaves 
show abundant evidence of larval depredations throughout the growing season. It is 
somewhat grasslike, yet less stiff and harsh than the preceding species. It is a rare 
Potamogeton in the flora and has been observed in one place only, Spencer Lake, where 
it is found in a muddy substratum in shallow waters of more or less swiftness. The 
plant has a bushy habit of growth, branching widely toward the summit, a habit which 
tends to produce dense patches of these plants. At one place in the station it grows in 
such dense masses as to choke up the mouth of a small stream entering the lake. 

The plants are late in appearing among the other aquatic forms in the spring, 
lagging behind P. zosterijoliiis a month or more. The bushy habit of the plant begins 
to show itself early in the summer, when branches arising near the base of the plant 
ramify toward the top until the characteristic bushy habit is attained. Fruit is pro- 
duced abundantly, but doubtless an equally important structure in the reproduction and 
distribution of the species is to be found in the large winter buds. These appear on the 
much-branched stems in great numbers and differ in no essential respect from those of 
P. zosierijoHus except that they are much less stiff". As in the above-mentioned species, 
they fall away from the parent plant when mature and sink to the bottom. Like 
P. zosterifolius , too, there is characteristic simplicity in the underground system. The 
mature plants which have been collected show no tendency to produce ramifications in 
the substratum, nor any indication of a perennial habit, but the plants become readily 
propagated vegetatively by means of winter buds or hibemacula. 

POTAMOGETON' FILIFORMIS. 

A habit sketch of this plant is shown in figure 36. Morong (1893) states that this 
is a rare species in the United States. One collection only was obtained. The specimens 
were found early in July near Canoga on Lake Cayuga, where the plant flourished in 
shallow water and among calcareous rocks along the shore. The plants were short and 
bushy in habit and bore abundant fruit. In all cases the erect axes developed from a 
tuberous rootstock which, judging from the numerous erect shoots that grew therefrom, 
is the common method of vegetative propagation in this species. The tubers (fig. 37) 
occurred in series of 3 to 5 on the rootstock. Although no opportunitv was afforded 
for studying this plant during the successive seasons, it is deemed worth while to 
record the obser^'ations of one collection of plants, since this species of Potamogeton 
is unique in its habitat and promising in the possibility of seed and tuber production. 

POT.\MOGETOX PECTIX.\TUS. 

This species possesses many important characteristics which recommend it to the 

culturist of aquatic plants. It is one of the most abundant and widespread of the 

Potamogetons. P. pectinaius is regularly found in quiet waters, though it has a variable 

habitat in other respects, occurring in a substratum that is sandy or muddv and in waters 

86309°— 1.5 3 



266 BULLETIN OF THE BUREAU OF FISHERIES. 

that are deep or shallow, fresh, salt, or brackish. It is also extremely variable in growth 
habit. Two of its remarkable lorms which occur in Lake Cayus^a and its environs and 
which Dudley (1886) describes as a slender form" and a gigantic form'' are included in 
the present investigation of this species. 

P. pcctinatuv, the species which is common everywhere, is among the first of the 
Potamogetons to sprout in the spring, making its appearance early in April. Of such 
plants which appeared early in the season, over a hundred individual specimens were 
uprooted to determine the agent of propagation. In all cases these plants developed 
from tubers which were buried in the mud or sand. Figure 38 shows the general habit 
of growth from these reproductive structures. The new plant quickly establishes itself 
bv developing simultaneously with shoot formation an extensive subterranean system 
of stems, which in turn send up leafy shoots in great numbers. By this ramification of 
the underground stems, P. pectinatus encroaches upon the soil so effectively as to produce 
dense patches of growth, to the exclusion, in some cases, of other species of aquatics. 
The plants bear fruit more or less abundantly, but, in general, tuber formation doubt- 
less equals or surpasses seed production. 

Tubers of various size occur, the size being dependent, more or less, on the nature 
of the environment. The largest and finest specimens were found at North Fairhaven 
in the quiet waters of Sterling Creek, where P. pectinatus forms a part of an equatic 
meadow renowned for its luxuriance of vegetation. These large tuber-bearing plants 
grow in the rich, mucky substratum at a depth of 6 to 10 feet in association with 
Elodea canadensis, Myriophyllum spicatum, Ceralophyllum demcrsum, Utricularia vulgaris 
var. A mericana,Nymphea advena and other Potamogetons, such as ampiif alius and zosteri- 
jolius. In this situation the plants are rapidly propagated from the tubers. On June 
2 1 several specimens were collected which illustrate the complete cycle of tuber forma- 
tion. Plants retained intact the old tubers, the new shoot — a tall, leafy, erect axis 
bearing in some cases a floral spike — and the new rootstocks bearing tubers. On 
many plants in this most favorable environment the tubers were greatly in excess of 
the matured fruits, and often the only reproductive structures. The plant dies down 
early in autumn. In October attempts were made to collect underground stems to 
determine, if possible, a perennial habit in this region. Only portions of the rootstock 
were secured, but in every instance disorganization had progressed to a considerable 
extent. The appearance of the tuber in the spring, when many of the plants were 
uprooted and observed with shoots growing from them, indicates a complete and 
natural separation from the parent stem, probably in the autumn. It may be inferred, 
then, that the tubers are the only vegetative structures that do survive the unfavorable 
growing season. 

The slender form described by Dudley (1886) was found still occupying the same 
region in Cayuga Lake where it was observed by him many years ago. The plants 

o 1007. var. (?) with slender elongated stems ( i to i ' ^meters) ; nodes remote, as are the whorls of the spike, whose peduncle 

is usually over one-Iourth meter long. Leaves few and slender, plants sometimes proliferous. Near the lighthouse, Cayuga L. 
Dr. Robbins "found no parallel for this remarkable form," in his own observations. Dudley, William R.; The Cayuga Flora. 
Bull. Cornell Univ. (Science), p. 107. 

& looS. var. (?) a gigantic form growing in deep water northwest and northeast of the lighthouse. Cayuga L. Not yet 

found in flower or fruit, though examined more or less frequently during 10 years past. It is frequently proliferous, especially if 
detached. It grows in banks, the plumelike bushy tops reaching the surface of the water. The leaves and sheaths are similar to 
P. pcctmatus. except in length. Dr. Robbins remarked that he had "nothing that comes near to it in length of leaves — usque ad 
10." Stipules are usually much shorter than in P. pectittulus. Specimens were obtained in 1S74 from 4 to sJi meters long. This 
form was also noticed by Mr. H. B. Lord, probably somewhat earlier than 1874. Loc. cit. 



POTAMOGETONS IN RELATION TO POND CULTURE. 267 

grew in banks in sand and silt bottoms at a depth of 5 to 7 feet. They were quite 
unmixed with other aquatics. In July and early August the long heavily fruited 
spikes floated in dense masses at the surface and gave to these areas of the water a 
characteristic brown look. Proliferations were not found on these plants during the 
summer; fruits, however, were more abundant than on any other form of pectinatus. 

The gigantic form of pccHnatus grows in deep water. Plants 8 feet long are com- 
mon, although many average but 5 feet at the end of the growing season. This form 
grows in a substratum of sand and silt at depths varying from 6 to 1 2 feet in a region 
of the lake exposed to a more or less constant sweep of the wind. The plants, there- 
fore, which grow practically to the surface of the water, are subjected at times to 
vigorous wave action. Altogether these environmental conditions favor a growth of 
remarkable luxuriance. The plants grow in banks, and so thickly as to preclude the 
possibility of encroachment by other forms of vegetation, though in shallow places, 
where the growth becomes sparser, a few scattered representatives of P. crispus, 
P. perjoliatus, and Heicranihera diibia occur. 

This form of pectinatus begins growth early in the spring. In May, 191 3, the 
plants already approached the surface of the water. On June 21, 1913, a plant bearing 
a single floral spike was found, although in several collections made thereafter neither 
flower nor fruit was obtained. This appears to be the first record of a floral spike on 
this form of pectinatus. From the collections made in November a few tubers were 
found on the tips of the foliage sprays of the plants that were uprooted from their 
natural moorings, although they were found more commonly on sprays that were floating 
in the drift. This latter observation is an agreement with Dudley (1886), who observed 
and described this form in Lake Cayuga. No rootstocks were secured, since attempts 
to uproot the plants at such depths with a grapple resulted always in breaking the 
stem just short of the subterranean system. This appeared to be embedded firmly and 
deeply in the substratum, at least more deeply than the length of the grapple teeth, 
which measured 4 inches. However, the bases of the erect stems, the parts which 
develop just above the rootstocks, possessed remarkable examples of proliferation. 
Thickened runners, more or less contorted, arose from leaf axils at the bases of the 
erect stems (fig. 50, A), terminated by large, elongate tubers. The bases of the stems 
were hard and woody, more especially so in the regions where they became detached 
from the underground system. This condition suggests a continuation of the woody 
structure in the subterranean parts. It may be inferred perhaps, from the general 
habit of the plant and the attendant conditions of growth, that the rootstocks are per- 
ennial, and that the basal runners, which bear in abundance large tubers and green 
shoots, are the chief propagative structures of this form of pectinatus. 

POTAMOGETON ROBBINSII. 

Although this Potamogeton is less well known than the other species, it is 
destined to be regarded as an important aquatic forage plant, first, because it is very 
prolific, and, second, because the foliage is very generally eaten. The habitat of this 
species, where it has been under observation, is not unlike that of P. amplijolius, with 
which it is often found in association. It has been obser\-ed in the quiet waters of lakes 
and ponds at depths of 3 to 5 feet in a substratum of rich, black mud. The stems 
ascend from a somewhat creeping base and branch profusely in a more or less two- 



268 BULLETIN OF THE BUREAU OF FISHERIES. 

ranked arrangement, forming large, broad, flat sprays of foliage, which often cover the 
bottom in large patches. It is the rarest of all Potamogetons to fruit, at least in the 
situations where it was observed, but because of the tendency to branch profusely 
propagation is readily effected. The branches, especially those whose internodes remain 
short, become thickened and hardened through the storage of starch, and when 
detached function as propagative structures. This enlargement and induration may 
occur also at various points along the main a.xis that bears the propagative branches, 
so that the final dismemberment of the whole plant provides enormous possibilities 
in the multiplication of the species. Dismemberment may occur in the autumn, but 
the plant is hardy, and this natural separation of parts may be deferred till spring, 
then long rootlets develop at the nodes and establish the plant at once. The plant is 
tardy in beginning its growth in the spring, but this tardiness in growth is obviously 
advantageous to a plant that propagates mainly by vegetative means in the manner 
of this species. Moreover, a very material advantage accrues in that the full and 
complete foliage of this Potamogeton appears late in the season when man)' other 
aquatics, including Potamogetons, show signs of decay. Growth occurs during the 
winter. It is not great, however, and manifests itself only in a slight elongation of the 
branches, producing fresh, green tips of foliage, which are foraged upon by aquatic 
herbivores almost as fast as the leaves appear. 

SUMMARY OF CULTUR.AL FE.ATURES. 

The Potamogetons which yield important forage products fall into two groups: 
Those which produce abundant herbage in their leaves — P. americanus, amplifolius, 
perjoliatus, crispiis, and Robbinsii — and those which develop a large supply of starchy 
food products in the tubers and tuberous rootstocks — P. pectinatus, filiformis, and 
heterophylliis. 

The species which grow best in the currents of streams are P. americanus and 
obiusifolius; in deep water, P. pectinatus, especially the slender and gigantic forms of 
Dudley; in calcareous regions, P. heterophyllus and filiformis; in exsiccated places, 
P. heterophyllus. 

The species appearing early in the spring are P. americanus , zosterifolius , pectinatus, 
heterophyllus, crispiis, and amplifolius; those growing late in the autumn and continu- 
ing throughout the winter are P. crispns, amplifolius, and Robbinsii. 

Abundant fruit is produced in P. perfoliatus, obtusifoliiis, and filiformis, and on 
pectinatus in most situations. Vegetative reproduction occurs freely in all species. 
The important vegetative structures are: Winter buds or hibernacula in P. obtusifoliiis 
and zo.fterif alius; modified branches in P. crispiis and Robbinsii; tubers in P. pecti- 
natus and filiformis; tuberous rootstocks in P. heterophyllus, and subterranean buds in 
P. americanus, amplifolius, and perfoliatus. 

NATURAL AND ARTIFICIAL PROPAGATION. 

The natural propagation of Potamogetons has been touched upon in a general survey 
of life conditions, and it has been seen that these plants propagate freely by means of 
various vegetative structures. At this point it is desirable to consider this method of 
propagation in greater detail, and to present data which will afford a means of com- 
parison between the general seed habit and the tendency to produce vegetative propa- 
gative structures. 



POTAMOGETONS IN RELATION TO POND CULTURE. 269 

PROPAGATION BY TUBERS. 

A conspicuous method of vegetative propagation is seen in the development of 
plants from tubers in P. pectinatus and P. filijormis. The tuber-forming habit of 
pectinatus has been described by Irmisch (1858), who carefully worked out the morpho- 
logical details of the tubers in terms of the ordinary stem structure. His figures illus- 
trate the development of tubers on detached parts of leafy stems, on the erect axis, and 
on the underground stems. It is not clear from which forms of pectinatus these drawings 
were made. In general, however, they bear a close resemblance to our most common 
representative of pectinatus, though no hint of the variability in this species is given 
beyond the fact that some plants were collected in deep water, and that the tubers 
were varied in shape, some being more cylindrical than others. 

The work of Sauvageau (1894) confirms the observations of Irmisch as regards the 
tuber-forming habits of pectinatus, but this investigator also makes no allusion to the 
remarkable forms that exist in this species. His drawings, moreover, are, as he states, 
modifications of those by Irmisch. Both of these workers in this field recorded the time 
of tuber formation to be in the autumn. Jepson (1905) suggests an earlier development 
for those on the rootstock and the erect stem. He says: "The slender threads which 
develop one, two, and even three tubers at the end, are not only borne on the horizontal 
rootstocks and on the soil at the bottom of the ponds, but are also produced on the 
upright stems, and at the end of the season on the uppermost leafy portion." 

Regarding the presence of tubers on rootstock, stem, and spray, the present investi- 
gation is confirmatory. Tubers have often been observed on all these parts of the plants. 
Additional figures and observations relate more especially to the season in which they 
occur and to their artificial propagation. Collections of plants made on the 15th of May, 
1913, and thereafter throughout the growing season, show the presence of tubers in great 
numbers on the proliferating shoots of the rootstocks. Many of these tubers are well 
grown in May, though others subsequently arise on the extensions of the subterranean 
system which develop after this time. 

Figure 41 represents the basal part of a small immature plant of P. pectinatus col- 
lected in shallow water June 20, 191 3. ilany plants at this time were more nearly 
mature and bore larger tubers, but it seemed desirable for illustration to select a small 
plant because in such all parts may be preserved intact during the collection of material, 
a task that is attended with considerable difficulty when the plant has attained a large 
size and great complexity of parts, especially in the subterranean region, where the 
underground sterns are exceedingly brittle and tender. This figure (fig. 41) illustrates 
the general sequence of growth in what may be termed the typical vegetative life cycle 
of the plant. The order of development is as follows: The production of a leafy, erect 
shoot (C) from the tuber of the preceding season (A); the growth of the horizontal axis 
or rootstock (D); and the production of the stolon-like branch or runner which in turn 
bears a tuber or tubers at the end (B). 

As the season progresses the tubers become solidly packed with starch in sufficient 
amount, apparentl\% to bring the plants developed from them to a very advanced stage 
of growth, at least to render them quite independent of the soil for a considerable length 
of time. Figure 45, B illustrates the typical condition in this respect when tubers sus- 
pended in aquaria without contact with the substratum produce the future propaga- 
tive structure. Thus the continued dependence of the plant upon the stored starch in 



270 BULLETIN" OF THE BUREAU OF FISHERIES. 

the tuber would seem to be advantageous, especially if growth occurred under untoward 
conditions. 

The tubers, hardened by the great quantity of starch that is packed into the tissues, 
nonnally pass through the winter in a dormant state. This, however, is quite easily 
disturbed, and by supplying continuously ordinary room temperatures the tubers may 
send forth shoots as early as October. Figure 45, noted above, illustrates such a response 
to growth conditions, the plant having been developed between the dates of October 22 
and December 20. 

The propagation of tubers in aquaria has shown that when tubers occur in twos, for 
example, figure 40, the larger one develops the shoot. The smaller one has never been 
seen to sprout unless by chance it became detached. In that case it developed an 
individual plant. It has been frequently observed that plants of this species when 
propagated in aquaria never attain their full size or vigor when deprived of a soil sub- 
stratum, an observation that is in accord with the results of Pond's (1903) experiments 
on rooted aquatic plants. 

The remarkable versatility of P. pectinatus as regards the origin of tuber-bearing 
runners has been clearly shown by Irmisch (1858). There is, moreover, in each of these 
situations, on rootstock, stem, and spray, a considerable variation in size and number of 
tubers. For example, an underground stem or rootstock may develop them at the ends 
of slender, stolon-like branches which arise from the axils of fertile nodes as shown in 
figure 43. These have been found singly or in pairs, large or small, depending upon 
the richness of the substratum and the size of the plant. Again, the rootstock itself may 
be terminated by tubers which occur singly, in pairs (fig. 42), or in threes (fig. 39). 
Plants bearing rootstocks of this character have been collected at various times during 
the growing season, and from each collection the specimens have shown comparatively 
short underground stems without other tuber-bearing structures. Some rootstocks 
have shown no tendency to produce tuber-bearing runners or tubers at the end of the 
horizontal axis, but send up a succession of leafy shoots from the fertile nodes. It is 
suspected, however, that had such plants been undisturbed tubers might have devel- 
oped, especially since at the base of these upright shoots there was always a bud, either 
latent or showing a tardy development. 

In autumn pectinatus develops tubers on the leafy spray. They are generallv 
smaller than those which occur on the rootstock, but quite conspicuous because of their 
pale, yellow color. They are borne singly or in pairs at the ends of runners that are 
bright green and stouter than the stems from which they arise (fig. 44, B, C). These 
structures are readily distinguishable about the time the plant begins to show signs of 
decay. They may occur on attached or detached parts of the plant. The remarkable 
prolificity of these sprays is a characteristic of this species. Repeatedly detached 
parts of the leafy spray have been placed in aquaria and tubers have been developed in 
abundance until the spray became completely disorganized. It is interesting to note 
that when this species grows in the currents of the stream the tendency to form pro- 
liferations on the leafy spray is conspicuously lessened, although portions of these plants 
when caught in the drift and carried to quiet water readily produce them in the new 
environment. 

For the most part tubers are more numerous on sprays devoid of fruiting spikes, 
although exceptions are frequent. In examples of this kind, figure 44, B, C, shows the 



POTAMOGETONS IN RELATION TO POND CULTURE. 27 1 

origin of tube-bearing structures, one arising near the base of the peduncle, the other 
soHtary from the axil of a leaf. Figure 44, A, is a detail of such a spray showing the 
usual character of the runner. Runners arise also on the lower parts of the stem 
(Irmisch, 1858). These, like many on the tips of the spray, may develop so late in the 
autumn that tubers never mature. What their fate is during the winter can only be 
conjectured. It is a fact, however, that when placed in aquaria they continue to grow 
slowly and eventually produce small tubers, or remain for a time in a quiescent state 
and then send forth leaves and other runners. 

In the gigantic form of lyrclinatiis (Dudley, 1886) the tubers are elongate and large 
in size. They are bom on runners at the bases of the stems just above the substratum 
of mud, and are therefore several feet beneath the surface of the water. Figure 61 
shows the entire leafy axis with a tuberous runner attached at the base of the stem. 
This is the normal position for what appears to be the chief propagative structure of 
this form of ptxtinatiis, and the usual condition at the approach of winter. The runner 
is seen in detail in figure 50. The tubers arc yellowish in color, and when stripped of 
scales, which envelop them at this season, appear as in figure 51. The remainder of 
the runner is dark green in color, more or less contorted and tuberous, and hardened 
throughout by storage of starch (fig. 50, B). Secondary runners bearing tubers (fig. 50, 
1 , 2) are additional features in what withal is a remarkable propagative structure. 
Peculiar tuberous internodes, transition stages, perhaps, in the formation of tubers, 
appear frequently and characterize the more hardened and resistant portions exclusive 
of the terminal tubers (fig. 52). On germination a leafy shoot and runner are pro- 
duced. Figure 55, an illustration of a similar feature repeated in a series, was devel- 
oped in an aquarium from the terminal tuber of a small runner. It illustrates how 
resourceful in the propagation of this species so small a structure may become. 

Young, green, leafy shoots arise from the fertile nodes of the runner (fig. 50, D) 
and doubtless function in perfecting the propagative structures of this persistent part 
of the plant, for at this time — that is, in the autumn — the leaves of the main axis 
begin to disorganize. The young shoots retain their greenness through the winter, 
remaining in a quiescent state meanwhile, and produce the main axis of the new plant 
the following spring. When these structures are transferred to aquaria, they pass 
through a winter-rest period, a period which is less easily disturbed, however, in this 
form of pectinalus than in others of the same species. Extreme plasticity is character- 
istic of various portions of the runner. Fertile nodes produce either tubers direct, or 
leafy tips, or runners, any one of which may in turn produce a runner. The tip of a 
secondary runner may produce a leafy shoot (fig. 53), and a tuber, instead of elongating 
its axis in the natural way, may develop precociously a reserve bud which produces 
the leafy stolon (fig. 54). 

As in pectinalus generally, the detached sprays of the gigantic form show a greater 
tendency to produce tubers than the attached ones. Likewise the runner is the im- 
portant structure which bears them. Such tubers may become very numerous. As 
many as 15 have been counted on a single plant (fig. 62). Detached portions of the 
plant bearing tubers float away in the drift, from whence they may or may not find a 
favorable place of growth in the spring. The tuber-bearing runners developed at the 
bases of the stems rarely become loosened from the tangle of vegetation at the bottom 
and must therefore repopulate the area year after year, encroaching but slowly on the 
surrounding region. 



2 72 BULLETIN OF THE BUREAU OF FISHERIES. 

P. filiformis represents a tuber-forming species which produces these propagative 
structures apparently in the manner of P. peclinaius. Since material was collected but 
once during the summer, no definite data can be recorded regarding the details of tuber 
formation beyond the fact that the plants develop from tubers, as the collected materials 
show (fig. 36, 37), and that these tubers, whether they occur singly or in a series of 
two or more, have a likeness to those of pccHnalus, in size resembling the common form 
and in shape approaching more neady the deep-water form. In details of structure the 
tubers of fi/iformis are similar to those of pcctinaius. Judging from the general habit 
of the plant it seems fair to assume that the tubers have arisen in the same way and that 
vegetative propagation would depend largely upon them. 

PROPAGATION BY TUBEROUS ROOTSTOCKS. 

The vegetative structures of P. hetcrophyllus tcrrcstris are illustrated in figures 10 
and II. Morphologically they are a series of more or less shortened and hardened 
internodes richly provisioned with starch. They are borne at the terminal portions of 
the underground stems. Well-developed buds, the incipient, erect axes, occur at alter- 
nate nodes of the structures, while the intervening nodes remain sterile, as in the case of 
undifferentiated rootstocks. Figure 8 represents a typical plant collected early in 
May. At this season the plant is still submerged. The tuberous rootstock of the pre- 
vious year sends up voung, erect shoots from the fertile nodes, and extends the growth 
horizontally by an elongation of the terminal bud to form the new rootstock. 

The underground stems acquire a distinctly tuberous appearance very early in the 
summer. At Mvers Point, where the collections were made frequently, the tuberous 
character became apparent at the time when drought conditions began to prevail in 
the pools; that is, when the water level was reduced to such an extent that the sub- 
merged, leafv shoots gave place to the later-formed, erect shoots topped with tufts or 
rosettes of aerial leaves which rest upon the mud. Figure 12 represents a plant of this 
kind. By comparing the plants shown in figures 12 and 16 the origin of the tuberous 
rootstocks is clear. In figure 16 tuberous structures appear at the ends of the new 
underground stems, B and C. This tendency to produce the tuberous growth may 
appear early when the plant is still submerged, though it may be deferred till drought 
conditions prevail, when the new type of leaves forming the rosette above the ground 
function to produce the abundant storage of starch which is found in the mature tuberous 
rootstocks. 

Some underground stems, throughout the growing season, continue to produce 
internodes nontuberous in structure (fig. 9), but they are exceptional rather than the 
rule. The tip of the rootstock that is destined to become tuberous generally shows 
this character very early. The internodes at the end do not elongate in the usual way, 
but appear serially in a more or less bead-like form (fig. 10 and 11). Figures 13 and 14 
represent the tuberous rootstocks partially developed. Figure 10 shows a fully mature 
one. These structures, and many others in similar stages of development, were col- 
lected in July and it is interesting to note that while some are only approximately mature 
others are fully so thus early in the season. In November all evidences of other plant 
parts have disappeared and the tuberous rootstocks only are left isolated in the mud, 
where they remain in a quiescent state through the winter. A typical structure, as it 



POTAMOGETONS IX RELATION TO POXD CULTURE. 273 

appears at the beginning of the winter, is seen in figure 11, although variations in the 
length and thickness of intemodes are not uncommon. 

Tuberous rootstocks have been transferred to aquaria, where the growth has cor- 
responded exactly with that exhibited in the natural habitat except in one respect, the 
development of aerial tufts of leaves. But the explanation of this omission in the 
cycle of development is clear, since the plants remained submerged in the aquaria. 
The period of desiccation not ha\dng been interpolated, it is assumed that the tuber 
formation progressed in a natural manner for the species. Figures 16 and 17, drawn 
from aquarium specimens, show how in the purely aquatic phase of its existence the 
natural habit of growth and reproduction in this Potamogeton is reproduced under 
artificial cultivation. 

PROPAGATION BY SUBTERRANE.'^N STEMS NOT TUBEROUS. 

Among the species studied, P. perfoliatus , P. amplifolius, and P. americanus are 
propagated in this manner. The plants are carried over the winter by means of the 
terminal portions of underground stems, which are generally stouter than the ordinarv 
ones and which bear conspicuous scaly buds. These buds are the incipient shoots from 
which the elaborate plant structures of the following season are developed. Sauvageau 
(1894) has figured this propagative structure for P. perfoliatus as he found it at the 
approach of winter. He states that the entire plant dies in autumn, except a few inter- 
nodes which bear the buds for the continuation of growth in the spring. In figure 
18 is represented a portion of an underground stem that sur%-ived the winter and pro- 
duced the first few intemodes of growth. The scales on the part that lasted through 
the year are distinctive in appearance. They are larger and looser than the ordinarv 
ones, black in color, and leathery- in texture (fig. 18, A.) 

In P. amplifolius perennial parts are also found in the underground stem. Figure 
7 represents the characteristic features of such a structure at the beginning of the winter. 
The young, erect shoots A, A, A, wit partially unfolded leaves at the tips, pass 
the winter unchanged and serve to promote rapid growth in the spring. The buds 
terminating the horizontal stems remain latent through the winter and on unfolding in 
the spring push out in all directions through the substratum. In these ramifications a 
subterranean system of interlocking stems and roots is developed that fixes the plant with 
exceeding firmness in the soil. 

In P. americamis vegetative propagation is accomplished by subterranean scaly 
buds which generally grow in pairs at the end of the rootstock (fig. 4 and 5). The general 
structure of the bud resembles that of P. perjoliahis. It is an incipient shoot, possessing 
a succession of very short intemodes and young leaves, with scales surrounding the whole 
a.xis. A small portion of the rootstock generally remains attached to the buds and 
persists through the winter. 

PROPAGATION BY WINTER liUDS. 

The \\inter buds afi'ord the only means of vegetative propagation which have been 
obser\^ed for P. zosterijolius and P. obtusifolius. These structures develop at the ends 
of the shoots. The terminal intemodes remain short and, becoming completelv cov- 
ered by closely overlapping leaves and stipules, form a hard, compact, cone-Uke bud. 



274 BULLETIN OF THE BUREAU OF FISHERIES. 

Such buds become conspicuous during the month of August. Later when they are 
mature they easily fall away from the parent axis, which thereafter dies down com- 
pletely. Being heavier than water, the buds sink to the bottom and by the middle of 
October they have either disappeared or have become entangled in the accumulations 
of Elodea, Myriophyllum, Ceratophyllum, etc., which still remain intact. In the dis- 
organization of this mass of vegetation, a gradual settling of the entangled buds takes 
place and they eventually find lodgment with the others in the substratum of mud, 
where they remain in a quiescent state till early spring. Such buds may properly be 
called hibemacula, since they pass through the unfavorable winter season in a state of 
rest. 

The general external aspect of the winter buds is seen in figures 33, 63, and 64. In 
size and form the two buds are quite similar but the leaves of obtusijolius are less stiff and 
harsh. In the internal structure of the bud (fig. 34) the typical branch-like character 
is apparent with the young leaves closely crowded toward the tip. 

Plants of both species have been reared in aquaria by anchoring the buds in sand 
or mud. The latter operation is not necessary, however, since mature buds sink naturally 
to the bottom, but it was a precautionary measure against the disturbance of buds under 
observation in aquaria. The plants of zosterijolius thus propagated did not bloom, but 
produced winter buds; those of obtusijolius bore flowers and fruit early in August. 

During the winter the loose leaves on the outside of the bud decay, but, on the whole, 
the entire bud is well preserved. This resistant character is more especially true of 
zosterijolius, in which many of the enveloping leaves of the bud persist long after the 
new plant has become established. In the spring the first sign of growth is manifested 
by a spreading of the inclosing leaves. Then follows the development of roots from 
successive nodes (fig. 35) and the elongation of the internodes at the tip of the bud. 
This elongation carries the young leaves forward and upward, and in a short time the 
general habit of the plant becomes apparent (fig. 65). The various stages in the growth 
of the bud in the spring are, in so far as they have been observed, similar in those two 
species of Potamogeton, except that obtusijolius lags behind zosterijolius. 

PROPAGATION BY BURS. 

P. crisfnis is the single example of such vegetative propagation. The first 
evidence of propagative structures by means of which the growth of this species is 
rapidly extended became noticeable early in May. At that time the so-called "burs" 
(fig. 22) made their appearance. They were enormously abundant, appearing in the 
axils of nearly all the leaves. Many of them became fully mature by the middle of 
the month, especially those which developed in pools of standing water where the daily 
temperature of the water was comparatively high. In the colder waters of spring pools 
and of the open lake these propagative structures, like the flowers and fruit, were 
retarded in development, maturing about two weeks later. As the summer advanced 
the development of the burs decreased until by the middle of July only scattered 
individuals were to be found. 

As a rule, the burs occur in the axils of the leaves. They may, however, terminate 
the growth of the axis (fig. 30). In this latter position they may occur in pairs (vSavau- 
geau 1894), often with a flowering spike. They may develop from the rootstock 



POTAMOGETONS IN RELATION TO POND CULTURE. 275 

directly (fig. 31), though this occurs but seldom. On the maturity of the bur detach- 
ment from the parent stem is an easy and natural process. The tissue just below 
fhe pointed base of the bur becomes softened and the burs fall away, either by their 
own weight or by accidental contact with other objects. On reaching the bottom, 
anchorage in the substratum is facilitated by the peculiar shape of the bur, a sharp- 
pointed, spindle-shaped structure that is heavier than water. A rest period occurs 
before germination takes place. This rest period is apparently a varied one, depending 
on the season when the bur is matured. Those which matured early in the season, in 
so far as it could be determined, germinated in the fall, and in October bore shoots 
from 6 to 10 inches long (fig. 59). Those maturing late passed the winter in the 
quiescent state and germinated early the following spring. 

The slender, spicular burs (fig. 21) described by Irmisch (1858) and by vSauvageau 
(1894) were found more or less commonly in the axils at the base of the erect stem, 
and always few in number compared with the stouter form. It is interesting to note 
in this connection that these spicular burs appeared more abundantly on the so-called 
"state" of P. crispus, a plant with flat, not undulate leaves, said to be a young state of 
crispus (Fryer, 1900). In one of the spring pools from which collections were made 
the spicular buds predominated on what appeared to be matured plants of this fiat- 
leaved form. The plants were never so vigorous looking as those in the other situations, 
and the appearance of the spicular burs upon them may be explained by dift'erences 
in habitat. Generally they appear to be poorly conditioned plants, and from observ-a- 
tions on their development it would seem that they are a starved state of crispus rather 
than a young state. 

The development of the large bur (fig. 22), which Sauvageau (1S94) described in 
part, has been observed in the field and in aquaria throughout the various stages, from 
its beginning as a small branch to its completion as a mature bur. Since the steps in 
the formation are essentially the same under natural or artificial conditions, observa- 
tions will be presented on the material under control in the laboratory. 

Vigorous looking plants were collected in the latter part of March and anchored 
in a soil substratum in aquaria with running water. Cuttings also were used, some of 
which were anchored in the soil and others allowed to float on the surface of the water. 
Three weeks later, short, stunted-looking branches appeared in the axils (fig. 26, A). 
They exhibited at once a noticeable thickness of the axis and later the peculiar 
denticulate appearance at the base of the leaves (fig. 22, a). When the diameter of 
the branch had become considerably augmented and the denticulate margin conspicu- 
ous, disorganization of the leaves commenced from the distal end and proceeded toward 
the base. Disorganization ceased at the tip of the denticulate base (fig. 22, a, i). By 
this time the basal portion of the leaf was hardened, thickened, and homy like the 
axis, and the entire structure presented the characteristic burlike appearance. Figure 
60 shows several small-sized denticulate burs in various stages of development. 

Essentially the two kinds of burs are similar, differing only in certain minor details. 
In the bur shown in figure 22 the leaf bases are large and always denticulate, the buds 
in the axils are relatively small, and the intemodes are short. In the spicular bur 
(fig. 2 1 ) the opposite is true. The leaf bases are small and spinous with a smooth margin, 
the buds are well developed, and the intemodes are comparatively long. A difference 



276 BULLETIN OF THE BUREAU OF FISHERIES. 

between them is also apparent in the time of occurrence and in position on the stem. 
Irmisch (1858) recognized a disparity between them and suggested a difference in origin, 
though he was not able to determine this for both forms. The spicular burs he found 
originating from the axillary buds of decaying, floating stems in autumn. The den- 
ticulate ones he found always mature and detached from the parent stem in muddy 
bottoms of pools. Sauvegeau (1894) describes and figures both forms of burs, giving 
their origin as well. My observations, however, are not in full agreement with their 
representation on the stem as expressed in Sauvageau's figures. According to his 
illustrations, both forms are abundant on the same branch and at the same season of 
the year. This has not been found to be the established order in vigorous and healthy- 
looking plants. Numerous collections of P. crispus indicate that when the denticulate 
burs are abundant — that is, in the early part of the growing season — the spicular burs 
are scarce, and if present on the same stem they are sparsely represented at the base of 
the axis. In every case the large denticulate bur seems to be the product of strong 
and vigorous-looking plants, and the spicular bur a result of poorly conditioned ones. 
That the spicular bur is a weakling would appear to be borne out by observations on 
their development. When grown in aquaria they have been found on sickly-looking 
plants and when germinating burs have been deprived of their vigorously growing 
shoots, small shoots bearing spicular burs have replaced them. In this instance a dis- 
turbance of the natural trend of growth would be the occasion of their formation. 
When the spicular burs genninate they produce shoots bearing leaves not crisped, 
but narrow and flat (fig. 25). 

The internal structure of the bur is fundamentally like that of the ordinary stem. 
No new features appear in the tissues of any part of the bur, but starch grains are 
present in such great quantities that the cells become distended with them. In the 
fully developed bur (fig. 71) the cells become so greatly expanded that the air cavities 
are practically obliterated. It is to these distended cells so compactly stored with 
starch that the hardened, indurated character is due. 

The accumulation of starch in the bur furnishes an abundant storage supply for 
rapid growth, after a rest period of greater or less prolongation, depending upon the 
time of formation. Burs formed early in the summer may germinate early in the fall, 
or, like those of later development, pass the winter in a quiescent state. Figure 23 
shows a stage of germination which is usual in the early spring. It is obvious from the 
general appearance of the shoots that burs of this character passed the early part of the 
winter in the resting stage. At the same time burs much more advanced in stage of 
growth (fig. 32) are frequent, and it is assumed that these are comparable to burs that 
germinated in the fall (fig. 59) and grew but little during the winter. In aquaria a varia- 
ble rest period is common. Under these conditions burs have been germinated after 
periods of six weeks and of three months. 

In the germination of a bur there are as many possibilities for the production of 
stems as there are axillary buds on it, although usually not all of the buds germinate. 
The greater number of burs bear but one shoot eventually, but several may begin 
growth and produce short shoots (fig. 23). By experiment it has been found that when 
a bur is broken into bits with one bud per node, each bud will produce a shoot. In 
the development of a plant from the bur, progress in the growth of a shoot manifests 



POTAMOGETONS IN RELATION TO POND CULTURE. 277 

itself first by the establishment of an erect axis, from which very soon a subterranean 
system arises in the manner shown in figure 27. Bv further extensions of these axes 
the number of branches is greatly augmented and the capacity for multiplication 
greatly increased. 

P. crispus, like most of the Potamogetons, propagates readily by detached stems. 
Many of these have been picked up in the drift along the lake shore where under favor- 
able circumstances some, doubtless, find lodgment and establish new centers of growth. 
Besides, in the spring there have been found leafy axes which, while still remaining 
attached to the parent stem, lie prone upon the muddy or sandy substratum and, be- 
coming rooted at the nodes, send up a long series of erect stems (fig. 20). In this manner 
P. crispus combines the rapid growth from stolons with the normal spread of the subter- 
ranean system and forms an effective means of possessing the soil. 

The large number of burs which are developed indicate that they are the chief source 
of distribution in this species. Some plants doubtless develop from seed, though they 
can not represent any great number of the whole since comparatively few seeds mature. 
To obtain some data on this point a large number of young plants were pulled up and to 
the most of them a bur was attached, an observation which shows that, for the region 
at least, this structure was the chief agent of propagation. From the standpoint of 
prolificity, P. crispus represents a desirable species for cultivation. It remains to be 
shown that this abundant herbage is of importance in the economy of aquatic life. Data 
relative to this are recorded under the heading "Economic aspects of Potamogetons." 

PROP.^GATION BV FR.\GMENTS OF STEMS. 

In P. Robbinsii the propagation occurs exclusively by vegetative means, depending 
upon a more or less complete dismemberment of the plant. This breaking of the plant 
into propagative structures does not take place at random, but occurs at very definite 
points throughout the leaf-bearing part of the plant. At intervals along the axes of the 
stems, a few internodes develop which are very short, and in them starch is stored 
so abundantly that they become hardened and stiff and noticeably thickened in diameter. 
At the limits of these indurated regions where the stems appear constricted, the tissues 
soften when the structures are mature, and dismembennent becomes a natural operation. 
The process of separation is similar to that which is met with in P. crispus and which 
causes the detachment of the bud from its parent stem. Besides the main axes of the 
plant which break up into many potential units, there are also numerous short, axillary 
branches which possess the characteristic feature of the propagative structure. The 
internodes are likewise short and stiff and conspicuously augmented by the deposition 
of starch. Moreover, they are always provided with a growing terminal bud, a feature 
which facilitates rapid propagation. When an axillary shoot becomes 6 or more inches 
long it behaves like the main axis of the stem eventually breaking up into several propa- 
gative structures. In figure 67 is represented a single branch showing the constricted 
appearance which distinguishes a stem bearing more than one propagative structure. 

In the spring, often before a general dismemberment of the plant occurs, very long, 
white rootlets are developed at the nodes (fig. 57). These rootlets ser^'e to anchor the 
new growth, whether it be an attached part of the plant or a scattered fragment of the 
stem. The provision for the initial growth in these fragments of stems lies in the storage 



278 BULLETIN OF THE BUREAU OF FISHERIES. 

of starch within the tissues. iStarch is so abundant that the air cavities are considerably 
reduced by the distension of the cells (fig. 71). In portions of the stem where the tissues 
are not obscured by the deposition of starch, it is seen (figs. 69, 70) that mechanical tissue 
is scattered through the stem in greater abundance than is common in the other Pota- 
mogetons, sen.-ing to support the heavy sprays of foliage and to give the rigidity of stem 
which is characteristic of this species. 

In P. amplijolins the tip ends of the branches function as propagative structures in a 
manner similar to P. Robbinsii (fig. 58). These structures appear in the autumn devel- 
oping onlv at the tips of the branches. The intemodes are short and thick and densely 
packed with starch. At the end there are a few partially unfolded leaves which con- 
tinue to grow slowly or, at least, remain green all winter. These rapidly expand when 
the roots develop in the spring and the entire structure forms an effective and rapid 
means of propagation. 

PROP.\G.\TION BY SEEDS. 

While the main purpose of this paper is a consideration of the vegetative means of 
propagation, yet it is important by way of comparison to present such data as are 
available on the propagation of these plants by seeds. In reviewing the literature on the 
seed germination of Potamogetons, it appears that Irmisch (1858) and Sauvageau (1894) 
have made the only contributions of importance." Irmisch figures the genriinating seeds 
and two small seedlings of P. nalans but otherwise gives no data concerning them. 
Sauvageau found that P. crispus, pcrfo/iatiis, and pcctiiiatus genninate in less than a 
year and that P. nalans remains donnant three or more years. No figures accompany 
his account of their behavior. 

In the course of the present investigation additional obser\'ations have been made on 
P. peclinatus and P. americanus. The seeds of both species were gathered in October 
and kept in cold storage through the winter. On January 24 seeds of each kind were 
placed in aquaria and kept at ordinary room temperatures. On February 14, the seeds 
of pcciinatHs began to genninate, but this process was very irregular, extending over a 
period of three or more weeks. These seedlings lacked vigor and nothing came of them. 
On March 15 other seeds of the same species were taken from cold storage and placed 
in aquaria as before. In this later planting germination was more uniform, the majority 
of seeds sprouting within a few days of each other. Subsequent growth was rapid and 
vigorous. It appears from the behavior of the seeds in the two experiments that the later 
planting is advantageous. Figures 46 and 47 represent seedlings of the second planting 

3 and 5 days old, respectively. Figure 48 represents a seedling of the same species 
about 10 days old, and figure 49, one about 3 weeks old. 

The seeds of P. americanus planted on January 24, showed no signs of life till May 5. 
Those of the second planting germinated between June 13 and 15. In this species also 
the later planting proved to be more successful. Figures 2 and 3 represent seedlings, 
respectively, 5 and 14 days old. When the seedlings were about 3 weeks old they 
were transplanted and kept in outdoor aquaria with running water till October. Figure 

4 shows one of these seedUngs which produced winter buds during the latter part of the 
growing season. These winter buds described in a preceding chapter are the vegetative 

f In a recent publication by Esenbeck the seedlings of P. lotoratus are described. (Esenbeck, Ernst: Beitrage zur biologie 
der gattungen Potamogeton und Scirpu^. Flora, bd :. June. 1914. p. 151-312, fig. 59.) 



POTAMOGETONS IN RELATION TO POND CULTURE. 



279 



propagative structures characteristic of the species. All of the seedlings produced them. 
Figure 5 represents the first shoot in a germinating winter bud. It may be assumed from 
the general behavior of the seedlings and the growth from the hibernacula that in this 
species vegetative structures only are matured the first year, and that seed formation 
is deferred at least until the second year. 

At present definite knowledge regarding the young stages of Potamogeton, in 
general, is very meager and this is doubtless attributable to the fact that the plants are 
small and inconspicuous the first year and fail to develop fruit until one or more vege- 
tative reproductions of the plant have taken place. 

PRODUCTION OF SEEDS AND VEGETATIVE PROPAGATIVE STRUCTURES. 

The abundance of P. crispus and P. pectinatu<: in the local flora have made it possible 
to observe the relative production of seeds and vegetative structures in a considerable 
number of these plants. Besides, the formation of the conspicuous vegetative structure 
in both species is practically synchronous with seed formation. The observations on 
mature plants selected at random form the basis of the following tables: 

Tabulations of Propagative Structures in Potamogeton crispus, June 16, 1913. 

(a) bur formation. 



Number of 
plants. 


Denticulate burs. 


Spicular 
burs, num- 
ber. 


With burs 
only, num- 


Plants with both burs 
and floral spikes. 












ber. 


Burs. 


Floral 
spikes. 






































3 




















4 










4 


3 










3 


















S 






II 














6 




















8 








•■ 


8 
8 








8 








13 


9 
9 

II 

12 

15 


9 
10 
10 
10 

II 
12 

13 

15 








21 




7 




100 


III 


U5 


32 


30 



28o 



BULLETIN OF THE BUREAU OF FISHERIES. 



Tabulations ok Propagative Structures int Potamogeton crispus, June i5, 1913 — Continued. 

(B) SEED FORMATION. 



Plants bearing sterile spikes. 


Plants bearing fertile spikes. 


Number of 
plants. 


Number of 

spikes per 

plant. 


Number of 

flowers on 

spike. 


Number of 
plants. 


Number of 

spikes per 

plant. 


Number of 
fertile 

spik es per 
plant. 


Number of 
seeds set. 


12 

10 
16 
6 

2 
3 
I 


I 
2 

3 
4 

S 
6 

7 


6-7 

4-7 
5-8 
S-9 
5-8 
5-7 
5^7 


4 
3 
6 
3 
I 
I 
I 


I 
a 
3 
4 
6 

3 
9 


2 
I 


2-4 

1-3 

1-5 

2-3 

3 

6 

I 


50 


139 


... 1 18 

1 


S3 


19 





Table A shows a preponderance of burs over floral spikes; table B, a preponderance 
of sterile spikes over fertile ones. A comparison of the tables A and B shows that bur 
formation exceeds seed production; that is, the important mode of increase is by vegeta- 
tive means. It should be remembered in this connection, however, that the bur which 
is the most conspicuous is but one of several vegetative structures contributing to the 
rapid extension of this species, and that seed production is, therefore, even less important 
relatively than the tables suggest it to be. 

TABiaATION OF PrOPAGATIVE STRUCTURES IN PoTAMOGETON PECTINATUS, SEPTEMBER 30, 1913. 



Number of 
plants. 


Number of fruiting 
spikes and tubers on 
same plant. 


Number of 
fruiting 


Number of 
tubers 
only. 


Number of 


Number of 
tubers on 
subterra- 
nean stems. 


Fertile 
spikes. 


Tubers. 


spikes only. 


stolons. 


t> I 

2 

3 




2 

I 
2 

5 

I 
3 
6 




17 
6 

7 
12 

3 
11 
2 




4 


10 

iS 
25 
5 

15 
8 






(«) 

I 

(«) 

{«) 

C«) 

(«) 

(«) 

(^) 

(^) 

I 

2 

I 

('') 

(«) 

r 

6 

(«) 

4 

(«) 

(«) 

3 

5 


35 1 24 




I 




86 


3 




43 



1 Imperfect record. 



'' This plant bore one sterile spike. 



The fertile spikes of P. pcctinatus produce, in general, from lo to 15 seeds. The 
tubers occur singly, in pairs, and in threes. Bearing these possibilities in mind, the 
tabulation of P. pectinatiis indicates a close approximation to equalitv in the produc- 
tion of seeds and tubers. The small number of plants from which the data were collected 
is an objection which could be justly put forward, yet the results conform in general 
with field observations in restricted areas where the common form of pectinatus 



POTAMOGETONS IN RELATION TO POND CULTURE. 28 1 

predominates. Propagation by tubers is, as we have seen, the more rapid method and 
the one which produces a luxuriant foliage early in the growing season. 

In view of the obser\-ations and experiments, it is clear that in any project in which 
the propagation of Potamogetons is an important feature, success will be measured by 
adherence to the general principle that vegetative reproduction is the dominant mode 
of increase in the genus Potamogeton. 

ECONOMIC ASPECTS OF POTAMOGETONS. 

In the study of the various phenomena attending the propagation of Potamogetons 
opportunity was afforded to observe, more or less closely, various aquatic animals which 
abounded on these plants. Their presence in such great numbers suggested the pos- 
sibility that the Potamogetons might play an important role in the economy of life 
beyond that of mere shelter and support, or other mechanical and indirect relations 
which have been ascribed to the larger aquatic plants for many years. 

It has been stated by Pond (1905) that — 

The larger aquatic plants, as such, are, while living, little used as food by aquatic animals, yet they 
greatly increase the surface available for the attachment of microscopic plant 'orms, which are eaten 
by smaller animals, and the latter in turn by the fishes. 

In the very recent publication by Shelford (1913), bearing on the life relations of 
aquatic animals, but little importance is attached to the larger aquatic plants beyond 
the various mechanical and indirect relations that have so long been attributed to 
them. He says: 

The smaller aquatic animals are commonly either alga-eaters or predatory-. The larger aquatic 
animals are commonly predatory or scavengers. The rooted vegetation is eaten only to a small extent. 
Small floating or swimming plants and animals are the basis of the food supply of larger animals. We 
could probably remove all the larger rooted plants and substitute something else of the same form and 
texture without greatly affecting the conditions of life in the water; that is, so far as the life habits of 
the animals are concerned. * * * Plants in water are of particular use to animals as clinging and 
nesting places. 

Recent research bids fair to modifj' these generalizations by Shelford. Such a 
relation as Pond describes has frequently been obser\-ed in P. pcctinatus in the autumn 
when myriads of midge (chironomid) cases have been found applied to the leaves (fig. 56). 
The leaves are not eaten but they are thickly covered with diatoms and other small 
algae which, doubtless, afford foraging materials for the larvse. A small caddis fiy 
(hydroptihd) lar\'a, with characteristic elliptical case, has also been observed in con- 
siderable numbers in the same relation with pectinatiis , the larvae apparently feeding 
on the epiphytic algal growth. The lar\-se of both of these insects, after wintering on 
the algal-covered leaves, have emerged as adults in the spring. Other midges and caddis 
flies, flies (aquatic Diptera), moths (aquatic Lepidoptera), and beetles (Coleoptera) 
have been found in great numbers on the various species of Potamogeton. The other 
smaller invertebrate animals most frequently seen on these plants are Crustacea, snails, 
and worms. 

Another interesting relation existing between the Potamogetons and aquatic insect 
forms is seen in the striking resemblance between the cases of a caddis fly (Leptoceridae) 
and the stipules of the leaf of P. americanus (fig. 75). The cases in which both larv'ae 
and pupae dwell are attached along the stems and leaves in so characteristic a manner 
as to become almost, if not quite, indistinguishable from the plant parts. 



282 BULLETIN OK THE BUREAU OF FISHERIES. 

Reighard (1894) has expressed in a table "a part of the imperfectly known relation- 
ships existing between the various groups of plants and the invertebrate animals on the 
one hand and the fishes on the other." One of the great gaps in the chain of relations 
therein expressed is a lack of definite knowledge concerning the role of the higher plants. 

Some definite research in this direction has been begun. Recent investigations 
on the food habits of aquatic insects have shown that the larger aquatic plants do 
serve as forage materials. According to Hart (1895), the larvse of Nymphula sp. (Para- 
ponyx), an aquatic lepidopterous insect, feed voraciously on Potamogeton natans. Need- 
ham (1907) mentions the presence of Nymplica advcmi in the diet of Cliironomns albis- 
tria, and Morgan (191 2) found that the higher plant tissues formed an important part 
of the stomach content of May-fly lan-ae. In view of these investigations the leaves 
and other edible parts of Potamogeton were closely scrutinized for evidences of their 
use as food. In my own investigations the first indication that the living tissues of 
Potamogeton was being eaten was seen in the young growing tips of P. crispiis, which 
had been transferred from a pond to an aquarium in the laboratory. The leaves of 
several plants were mined by a small larval form which proved to be a chironomid 
(midge). The characteristic leaf mine is shown in figure 72. Miss Tilbury (1913), 
who was working in the Cornell laboratory on the feeding habits of the midge, taking 
advantage of this obser\-ation, reared her species, Chironomus cayugce Johannsen, 
mainly on P. crispiis- and entirely on Potamogeton. 

On examining the leaves of other Potamogetons it was found that practically all 
species were foraged upon to a greater or less extent. Lar\'al depredations were most 
common on P. Robbin.ui. In this plant the aquatic lepidopterous larva Nymphula sp. 
{Paraponyx) is the chief herbivore, and so voracious is its appetite that a large proportion 
of the growing tips are constantly being defoliated in the manner shown by figure 68. 
Portions of the leaf are cut out also by the lar\-a, applied together by means of silk, 
and used as a protective case or retreat during the larv^al and pujial stages. Nymphula 
sp. is by far the most conspicuous lar\-a feeding upon P. Robbinsii, yet other important 
smaller forms are numerous. The limy incrustation that accumulates very freely on 
P. Robbinsii offers apparently especial inducements to certain case-making insects, as 
midges and caddis flies. vSuch lar\-E are exceedingly numerous on this species of plant, 
and the limy incrustation is the chief material used in the construction of the cases. 

A few of the chironomid larv'te that were common on P. Robbintii collected at North 
Fairhaven in October were segregated and fed exclusively on this Potamogeton. They 
passed successfully through the pupal and adult stages and proved to be the midge, 
ChironomoHS aberrans. The larval and pupal stages have been hitherto unrecognized 
in the life history of this species." 

The leaves of P. amplijolius were conspicuously mined by the dipterous larva 
Hydrellia sp. (Ephydridce). The pupae were collected on the leaves August 6. Several 
flies and their parasites were reared from them, emergence occurring between August 16 
and 20. The larva makes a wide, irregular mine through the leaf, and in each case under 
obser\'ation pupates at the end of the mine toward the base of the leaf blade where the 
edges naturally roll together and form a protecting furrow (fig. j^i)- Nymphula sp. 
{Paraponyx) is also common on this Potamogeton and many of the young leaves are eaten 
bv them. Oftentimes the larva cuts out a portion of the leaf for its case with the neat- 

Determinations of dipterous larvae have been made by Prof. O. A. Johannsen; of caddis-fly larvae, by Mr. J. T. Lloyd. 



POTAMOGETONS IN RELATION TO POND CULTURE. 283 

ness and precision of a leaf cutter bee (fig. 74), though usually there is less regularity 
of outline. 

On the floating leaves of P. americanus collected early in August were found eggs 
of Paraponyx and of chironomid." Those of Paraponyx covered broad areas of the 
under surfaces of the leaves and presented the appearance of minute six-sided cells of 
honeycomb, yellowish in color. In a few days the larvae hatched and began at once to 
feed and to cut portions from the leaves for larval cases. Fryer (1S88), in connection 
with his studies on P. fluitans, mentions that the larva of Nymphula {Hydrocampa 
potamoqaia) entirely destroy the floating leaves of this species, and thus indirectly 
induce the development of fascicles of leaves, structures which are analogous to the 
winter buds of P. obiwsifolius. The eggs of the chironomid, which were found on the 
leaves of P. aniericanus , were inclosed in small elongate cases blackish in color, suspended 
from the edges and from the underside of the leaf, and from the petiole. These eggs 
hatched within a few days, but their entire life history was not observed. 

The leaves of P. oblusifolius harbor a large number of chironomids, and apparently 
offer a valuable supply of food to many of them. A few of the larvae were segregated 
in small dishes and supplied with fresh leaves of this Potamogeton. An undescribed 
species of Chironomus was reared. Cricolopus trifasciahis and Tanypus flavellus were 
the most abundant species on the leaves. 

Other plant parts besides leaves were eaten. The tubers of P. pectinatus and the burs of 
P.crispiisweTe devoured by the larvae of Paraponyx and by the larvae of the Chironomidae. 

The underground stems of P. pectinatus * are provided with large and numerous 
air spaces (fig. 66), and these were found to be an important air-supplying source for 
the Donacia lar\-se. The lar\'£e attached to the subterranean stems of this Potamogeton 
were collected from the muddy substratum at North Fairhaven August 14, 1913. 
Stems on which the lars'se were not attached showed, quite generally, the characteristic 
punctures, or double scars, made by the caudal spines in tapping the air supplv. 

Jepson (1905) called attention to the value of the tubers of P. pectinatus in the 
diet of our wild game birds. He says, "The diving ducks, such as the canvasback 
and broadbill, eagerly seek these tubers, devoting most of their time to this pursuit 
until the duck-shooting season opens." McAtee (191 1) and Thompson (1913) in their 
researches on the diet of wild game birds have shown that a large percentage of the 
food taken is Potamogeton. 

The stomach content of 5 canvasbacks has come under my observation recently. 
One duck shot in October had been feeding in rich aquatic meadows where Potarao- 
getons flourished with Myriophyllum, Elodea, etc. Its stomach was tilled exclusively 
with tubers of P. pectinatus. Four ducks shot at the close of the season in January 
had apparently exercised a choice in the matter of food. Feeding in an abundant 
mixed vegetation, they had selected only Potamogeton — P. Fresii and P. pusilliis. 
The parts of the plants available were the winter buds which at this season have 
settled in the mud at the bottom along with the hibernacula of Myriophyllum, Elodea, 
and other aquatic plants. 

<> Duringsubsequentobservationsinjune, 1914, masses of eggs almost inimitein variety and number have beenfound attached 
to the stems and leaves of the various Potamogetons. It would seem that these plants, diverse as they are in habit and form, 
ofler especially suitable conditions for the attachment of the eggs of aquatic animals. The eggs of the water mite (Hydracarina) 
are exceedingly abundant. The eggs of insects that have been recognized are as follows: StratiomyiidEe. Coriscidae. Gyriuidse, 
Donaciinte. Hydrophylidae. PyralidEe. Cordulins (Tetragoneuria). Hydrobatids and Tricoptera. 

& Since this observation was recorded Donacia larvx have been found on the underground stems of P. americanus . 



284 



BULLETIN OF THE BUREAU OF FISHERIES. 



SPECIES OF POTAMOGETON AND THE ANIMALS FORAGING UPON THEM. 

To facilitate reference, a list is given of the species of Potamogeton, together with 
the smaller animals which have appeared to be intimately associated with them. Other 
forms of animal life were often found upon these plants, but none seemed to be so char- 
acteristically on their own ground, so to speak, as the forms listed below. Those 
animals are starred (*) which have been observed feeding on the living plant tissue. 

List of Pot.^mogetons and Small Animal Forms Associated with Them." 



Plant. 


Animal. 


P. americanus 


Insecta.. 


Diptera: 

Chironomidce (undetermined). 
Lepidoptera: 
Pyralidse- 

* Nymphula sp. (Paraponyx). 
Tricoptera: 

Leptocerida? — 
Two species. 




MoUusca. . 


Ancylus. 


P. amplifolins 


Insecta. 


Diptera: 

Ephydridae — 

* Hydrellia sp. 
Chironomida:— 






* Chironomus sp. 

* Tanytarsus sp. 
Tricoptera: 

Undetrmincd. 
Lepidoptera: 
Pyralida— 

* N>Tnphula sp. (Parapony-x). 




Mollusca.. 


Ancylus. 


P. perfoliatus 


Insecta. . 


Diptera: 

Chironomidse — 

* Tanytarsus sp. 


P. crispus 


Insecta. , 


Diptera: 

* Chironoraidae (undetermined). 
Lepidoptera: 

Pyralidce— 

* Nymphula sp. (Hydrocampa). 


P. zosterifolius 


Insecta. . 


Diptera: 

Chirooomidfe — 

* Tanytarsus sp. 
Lepidoptera: 

Pyralidae — 

* Nymphula sp. (Paraponyx). 
Tricoptera: 

Undetermined. 


P. obtusifolius 


Insecta. . 


Diptera: 

Chironomida? — 
* Chironomous sp. 
Cricotopus trifasciatus. 
Tanytarsus flavellus. 


P. pectinatus 


Insecta. . 


Diptera: 

Chironomidse — 

Tan>tarsus flavellus 
Cricopteris sp. 
Tricoptera: 

Hydroptilid:E (in autumn). 
Coleoptera: 

Donaciinc — 
Douacia sp. 


P. pectinatus 


Insecta. . 


Diptera: 


(Gigantic form) 




Chironomida? — 



P. Robbinsii . 



Crustacea. 



Vermes . 
, Insecta. 



Chironomous sp. 

Tanytarsus sp. 
Amphipoda (very abundant). 

Gammarus. 

Hyallela. 

Eucrangonyx. 

Nais (very abundant in autumn). 
Diptera: 

Chircnomidae — 

* Chironomus aberrans. 
Tanytarsus sp. 

Tricoptera — 

Undetermined. 
Lepidoptera: 

* Nymphula sp. (ParaponiTt). 



« A Potamogeton which came under casual observation only, P. Epthydrus. may be mentioned as an important addition to 
the plants actually foraged upon by msect larvae. Several specimens of this species of Potamogeton, collected at Spencer Lake 
in August, were quite thickly dotted with caddis-fly larvae (Leptoceridse), which were feeding upon the fresh green leaves. 



POTAMOGETONS IN RELATION TO POND CULTURE. 285 

The Mollusca — Planorbis, Limnea, and Physa — were common on all of the Pota- 
njogetons. 

These observations on the animal life associated with the Potamogetons afford 
an additional contribution to the biological relations of the Chironomidae, Pyralidas, 
Leptoceridoe, Hydroptilidae, and Ephydridae, groups in which one or more members 
have been observed in their feeding operations. Of these animals it has already 
been recorded by Reighard (1894) that the Chironomidae are an important fish food- 
Scattered reference is made by others of the value of aquatic insect larvae in the diet 
of fish. The fact that these insects eat the living plant tissue of the Potamogetons 
adds greatly to the importance of these plants from an economic standpoint. 

CONCLUSION. 

In all contributions bearing on the life conditions of the Potamogetons, the promi- 
nence of these plants in the shoal waters has been recognized, and where special effort 
has been directed toward the study of their life relations, an economic value has been 
ascribed to them. The present investigation affords further evidence of the economic 
value of these plants, and contributes the results of observation and experiment on the 
cultivation of several species. These results warrant the expenditure of additional 
thought and effort on what purports to be one of the most important resources of our 
lakes, ponds, and streams. 



BIBLIOGRAPHY. 

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AscHERSON, p., and Graebner, p!" 

1907. Potamogetonacese, Das Pflanzenreich 4 ,, n tS. t.w « 
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1911. Die Flora des Untersees. Stuttgart 
Bennett. ARTHtR. 

1880 Notes on pondweeds. Journal of Botany, p ,80 
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Chamisso and Schlechtend. 

1827. LLnnea, vol. 2, p. ir--2,, 
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tanique de France, t , p „<>.,,, ^ ^^ ^- ^""etm de la Soci6t6 Bo- 

Constantin, J. ' J- J5 oi-- 

Davis, Chas. A 

Dudley, Wii.u.«i R. ^ ^""^ °^ "'^P"'^ ^"■" 'W, p. 217-23,, pi. 60, 3 maps 

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Forbes, S. A. 

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1888. Notes on pondweeds. Journal of Botany, vol. .6 p 2-.-.-S 
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BULLETIN OF THE BUREAU OF FISHERIES. 287 

Gluck, Hugo. 

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288 BULLETIN OF THE BUREAU OF FISHERIES. 

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EXPLANATION OF PLATES. 

All of figures on Plates XXXIV-XXXIX, with the exception of tlie photo-micro- 
graphs, are photographs of plants floating in water, in aquaria, or in specimen jars. 

Plate XXII. 

Fic. I. Potamogeton amerkantis, seed, I'i times natural size. 

Fig. 2. Potamoyctoii americanus, seedling 5 days old. ifi times natural size. 

Fig. 3. Potamogcloi! americanus, seedling 14 d3.yii old, 1/ 2 times natural size. 

Fig. 4. Polamogeton americanus, seedling of four months, }2 natural size; A, winter buds. 

Fig. 5. Polamogeton americanus. germinating %vinter bud, natural size; the last two winter buds 
belated in development. Aquarium specimen. January 24, 1914. 

Fig. 6. Polamogeton americanus. rootstock with winter bud A, natural size. September. 

Plate XXIII. 

Fig. 7. Polamogeton amplifolius, rootstock, y< natural size; A, A, A, young shoots which continue 
to grow slowly through winter. November. 

Fig. 8. Polamogeton helerophyUm, submerged plant, J.^ natural size; A, tuberous rootstock; B, B, 
submerged shoots; a, b, and c, details of leaves. May 4. 

Fig. 9. Po/amoi^ftow Af/cTo/>/;;7/Mj, rootstock not tuberous, natural size. July 7. 

Fig. 10. Po/a»iO(;c/o« /;i';cro/'/;j//«f, tuberous rootstock, natural size. July 7. 

Fig. II. Polamogeton hctoophyllus, tuberous rootstock. natural size; A, A, incipient shoots 
November 17. 

Plate XXIV. 

Fig. 12. Polamogeton hcterophyltus, typical habit of land form, I'j times natural size. Terminal 
portion of rootstock tuberous. July 7. 

Fig. 13. Polamogeton helerophyllus, terminal portion of rootstock showing tendency to become 
tuberous, i}i times natural size. Jul)- 7. 

Fig. 14. Same, more advanced stage, i/i times nattual size. July 7. 

Fig. 15. Potamogeton /it/cro/)/!)7/i<.f, aquarium specimen, natural size; A, tuberous internode placed 
in aquarium in November; B, B. new shoots and rootstock. January 26. 

Plate XXV. 

Fig. 16. Potamogeton helerophyllus, aquarium specimen, natural size; A, B, C, D, new shoot and 
tuberous rootstocks in various stages of growth. March 14. 

Fig. 17. Potamogeton helerophyllus, aquarium specimen, natural size. 

Fig. 18. Polamogeton perfolialus, winter shoot showing elongation of intemodcs, natural size; A, 
leathery scale ; a, detail of scale. June. 

Fig. 19. Growing tips of same. 

Plate XXVI. 

Fig. 20. Potamogeton crispuf, recimibent branch, showing development of i-.ow shoots on old stem, 
J 2 natural size. March. 

Fig. 21. PotoHOf/t'/oH cm/>Hi', spicular bur, i^i times natural size. Aquarium. July. 

Fig. 22. Potamogeton crispus. denticulate bur, 3^ natural size; a, detail of leaf with denticulate 
base, 2 times natural size; i, line delimiting starch storage. 

Fig. 23. Po/amo^Won crw/>Mf, sprouting bur, i^'< times natural size. March. 

Fig. 24. Potamogeton crispus. denticulate bur with sprout, natural size. Aquarium. July. 

Fig. 25. Po/amo^f/oH cr;(/;!(j-, spicular bur with sprout, ,'2 nattiral size. Aquarium. July. 

289 



Fig. 


36- 


Fig. 


37- 


Fig. 


38. 


Fig. 


39- 



290 BULLETIN OF THE BUREAU OF FISHERIES. 

Pl.\tr XXVII. 

Fig. 26. Polamogclon crispiis. cutting showing bur devt-lopment. ';' natural size: A. immature burs. 
Aquarium. March 22-ApriI 7. 

Fig. 27. PotaniogetoK crispus. sprouting bur, showing {levelopnient of rootstock and erect shoots, 

natural size. 

Fig. 28. Polamogeton crispus. shoot with spicular bur at base, natural size. 

Fig. 2q. Polamogeton crispus, similar structure rooting above tip of bur. natural size. 

Fig. 50. Polamogeton crispus, biu" formation at tip of branch, I'i^ times natural size. Aquarium. 

Plate XXVIII. 

Fig. 31. Polamogeton crispus. subterranean stem, showing bur in axil of scale, natural size. June. 

Fig. 32. Polamogclon crispus, spnmlmgbuT, 3-:^' natural size. March. 

Fig. Si- Polamogeton zosterif alius, winter bud. .'4 natural size. October. 

Fig. 34. Potavwgeton zosierif alius, long section of winter bud, I's times natural size. 

Fig. 35. Polamogeton zosierif alius, winter bud sprouting. Vi natural size. April. 

Platb XXIX. 

Polamogclon filijormis. habit sketch. ■ 2 natural size. July. 
Patamogclonfiliformis. detail of tuberous rootstock. i ■4' times natural size. 
Polamogeton peclinatus, young plant developing from tuber A, ; , natural size. May. 
Polamogclon pcclinalus, series of tubers, slender form of Dudley, % natural size. 
Fig. 40. Polamogeton peclinatus, tubers, showing details of early growth, iji times natural size. 

P1.AT1; XXX. 

Fig. 41. Polamogeton peclinatus, tubers of two successive seasons; A, old; B, young; C. erect stem; 
D, subterranean stem; 1% times natural size. 

Fig. 42. Polamogclon peclinatus, terminal portion of subterranean stem, ly, times natural size. A 
condition which may be present from June to October. 

Fig. 43. Potamogelon peclinatus, mature portion of rtxjtstock bearing tuberous runners; A, tuber- 
bearing runner ; natural size. September. 

Fig. 44. Polamogeton pectinaltis, spray showing fruiting spike and tuberous runners. A, B, C, ;^ 
natural size; o, detail of runner; A, A, young green shoots. 

Plate XXXI. 

Fig. 45. Polamogclon pcclinalus. plant developed in aquarium, suspended in water, 1 2 natural size; 
A, old tuber which produced plant; B, young tuber. 

Fig. 46. Polamogclon pcclinalus, sprouting seed, 3 times natural size. 

Fig. 47. Same, later stage, 3 times natural size. 

Fig. 48. Potamogelon pcclinalus, seedling about 10 days old, outer testa of seed removed, 1^4 times 
natural size; a, inner hard testa, showing characteristic lid-like portion thrust open, i !< times natural 
size; b, seedling with hard testa of seed removed showing foot-like expansion. 

Fig. 49. Potamogelon peclinatus, seedling three weeks old, natural size. 

Plate XXXII. 

Fig. 50. Polamogeton peclinatus, gigantic form of Dudley, runner B, from base of erect shoot A, 
J-2 natural size ; C, tuber; D, D, D, young green shoots; 1.2, secondary runners. November. 

Fig. 51. Potamogelon pcclinalus, gigantic form of Dudley, tuber devoid of scales, I'j times natural 
size. 

Fig. 52. Polamogeton pcclinalus, gigantic form of Dudley, portion of a tuberous runner, natural size. 

Fig. 53. Potamogelon pcclinalus, gigantic form of Dudley, growing tip of secondar\' runner, natural 
size. 



EXPLANATION OF PLATES. 291 

Platu XXXIII. 

Fig. 54. Potamogeton /"ff/iwa/ui, gigantic form of Dudley, sprouting tuber, i'/ times natural size. 
Aquarium, February. 

Fig. 55. Potamogeton l>ecti)iatus , gigantic form of Dudley, tuberous runner, natural size. 

Fig. 56. Potamogeton peetinaius. spray, showing cases of chironomids. natural size. September- 
November. 

Fig. 57. Potamogeton Robbinsii. characteristic vegetative structure, rooting at nodes, iVj times 
natural size. May. 

Plate XXXIV. 

Fig. 5S. Potamogeton amplifolius, rooted tip of branch, a propagative structure. April. 

Fig. 59. Potamogeton crispus, germinating bin's. October. 

Fig. 60. Potamogeton erispus, burs in various stages of development. June. 

Plate XXXV. 

Fig. 61. Potamogeton peclinatus, gig.intic form of Dudley, erect axis of plant, 5 feet 2 inches tall, 
bearing runner at base of stem. November. 

Fig. 62. Potamogeton pectinatiis, gigantic form of Dudley, portion of leafy spray showing tubers. 
November. 

Plate XXXVI. 

Fig. 63. Potamogeton obtusifolius , winter buds. October. 

Fig. 64. Potamogeton obtusifolius, erect axes bearing winter buds. October. 

Fig. 65. Po/amof/t'/on zo.vfcrj/o/Mft, sprouting winter bud. Aquarium specimen. February-. 

Pl.\te X-XXVII. 

Fig. 66. Potamogeton peetinaius, cross section through stem, showing numerous air spaces. 

Fig. 67. Potamogeton Robbinsii, branch, showing points where dismemberment occurs, i, 2, 3. 

Fig. 6S. Potamogeton Robbinsii, branch defoliated by larvae of Nymphula sp. (Paraponyx). Larval 

cases, 1,2,3. 

Pl.^te XXXVIII. 

Fig. 6q. Potamogeton Robbinsii, photo-micrograph of section through old stem, showing arrange- 
ment of mechanical tissue. 

Fig. 70. Detail of fig. 6g. 

Fig. 71. Potamogeton crispus, photo-micrograph of section through stem of starch-filled vegetative 
structure; a, cell with starch grains. November. 

Plate XXXIX. 

Fig. 72. Potamogeton crispus, leaves, showing characteristic leaf mining of chironomids. 

Fig. 73. Potamogeton amplifolius, leaves, showing characteristic mines of Hydrellia sp.; a, b, pupa 
cases at end of mines. August. 

Fig. 74. Potamogeton amplifolius; a, h, leaves, showing circular pieces cut away by larva of Nym- 
phula sp. (Paraponyx); i, larva in case; c, dead leaf, showing cases of Chironomus sp. 

Fig. 75. Potamogeton americanus. spray showing attachment of cases of caddis fly (fam. Leptoce- 
ridae); a, case of caddis fly; b, stipule of leaf. June 31, 1914. 



BuLi.. U. S. B. 1'., iyi3. 



Pi^ATi; XXII. 




BuLi,. U. S. B. r., 1913. 



Platk XXIII. 




10 








r.iu.i.. IT. S. B. F., 191 V 



Pl.ATl-. XXIV. 




Bull. U. S. 11. !•'.. im.v 



I'LA-nc XXV. 



1(5 





Bull. IT. vS. B. I"., i.,,i3. 



I'l.ATK XX\'I. 




Bull. U. S. B. F., 1913. 



Pl.ATl. XX\'II. 




iJuLi,. V. s. ];. F., 19 1, V 



Pl.ATK XX\"III. 




Bull. U. S. B. F., lyi;,. 



Plate XXIX. 





Pl.ATH XXX. 




-SZ/- 



Bull. U. S. B. F., 1913. 



I'LA'i'h: XXXI. 




46 




49 






Bull. U. S. 15. F., 1913. 



Platk XXXTI. 




Bull. U. S. B. F., 1913. 



Plati: XXXIII. 




—"**:, 





55 




Bull. U. vS. B. F., ioi,. 



Blatjc XXXIV, 




58 




#- 


¥- * 





Bui.i.. U. S, r,. }<'.. lm;,. 



Pl.AT]- XXX\', 




02 




(iJ 



Bull. U. S. ]'.. I"., \ ',>:,. 



Plati.: XXX\'I. 




(;;] 





Go 



Bi'LL. U. S. rs. v., igi.v 



Platk XXX\II. 




(JG 




Bull. U. S. B. I*., igi;,. 



I'LATK XXXVIII. 




Btti.i.. it. S. R. F., iqi.v 



Pi.AT].: XXXIX. 





to 



72 




74 




to 



LIBRftRY OF CONGRESS 




